Illumination method and light-emitting device

ABSTRACT

To provide an illumination method and a light-emitting device which are capable of achieving, under an indoor illumination environment where illuminance is around 5000 lx or lower when performing detailed work and generally around 1500 lx or lower, a color appearance or an object appearance as perceived by a person, will be as natural, vivid, highly visible, and comfortable as though perceived outdoors in a high-illuminance environment, regardless of scores of various color rendition metric. Light emitted from the light-emitting device illuminates an object such that light measured at a position of the object satisfies specific requirements. A feature of the light-emitting device is that light emitted by the light-emitting device in a main radiant direction satisfies specific requirements.

CROSS-REFERENCE TO RELATED APPLICATION

This is a continuation of International Application PCT/JP2012/072144,filed on Aug. 31, 2012, and designated the U.S., (and claims priorityfrom Japanese Patent Application 2011-192140 which was filed on Sep. 2,2011, Japanese Patent Application 2011-192142 which was filed on Sep. 2,2011 and Japanese Patent Application 2011-223472 which was filed on Oct.7, 2011) the entire contents of which are incorporated herein byreference.

TECHNICAL FIELD

The present invention relates to an illumination method by which lightemitted from a light-emitting device including a semiconductorlight-emitting element that is a light-emitting element illuminates anobject, and to a light-emitting device including a semiconductorlight-emitting element that is a light-emitting element.

BACKGROUND ART

Recent advances toward higher output and higher efficiency in GaNrelated semiconductor light-emitting elements have been dramatic. Inaddition, active research is underway to increase efficiency ofsemiconductor light-emitting elements and various phosphors that use anelectron beam as an excitation source. As a result, power-savingcapabilities of today's light-emitting devices such as light sources,light source modules including light sources, fixtures including lightsource modules, and systems including fixtures are advancing rapidly ascompared to their conventional counterparts.

For example, it is widely popular to incorporate a GaN related bluelight-emitting element as an excitation light source of a yellowphosphor and create a so-called pseudo-white light source from aspectrum of the GaN related blue light-emitting element and a spectrumof the yellow phosphor, use the pseudo-white light source as anillumination light source or create a lighting fixture that incorporatesthe pseudo-white light source or, further, fabricate a lighting systemin which a plurality of such fixtures are arranged in a space (refer toPatent Document 1).

Among packaged LEDs (for example, those that include the GaN relatedblue light-emitting element, the yellow phosphor, an encapsulant, andthe like in a package material) which are a type of an illuminationlight source that can be incorporated into such modes, there areproducts with luminous efficacy of a source as a packaged LED exceeding150 lm/W in a correlated color temperature (CCT) region of around 6000 K(refer to Non-Patent Document 2).

Furthermore, similar advances toward higher efficiency and greater powersaving are being made in light sources for liquid crystal display (LCD)backlighting and the like.

However, many have pointed out that such light-emitting devices aimingfor higher efficiency do not give sufficient consideration to colorappearance. In particular, when used for illumination purposes, “colorappearance” when illuminating an object with a light-emitting devicesuch as a light source, fixture, system, or the like is extremelyimportant together with increasing efficiency of the light-emittingdevice.

Attempts to address this issue include superimposing a spectrum of a redphosphor or a red semiconductor light-emitting element on a spectrum ofa blue light-emitting element and a spectrum of a yellow phosphor inorder to improve scores of a color rendering index (CRI) (CIE (13.3)) asestablished by the International Commission on Illumination (CommissionInternationale de l'Eclairage/CIE). For example, while an average colorrendering index (R_(a)) and a special color rendering index (R₉) withrespect to a vivid red color sample for a typical spectrum (CCT=around6800 K) that does not include a red source are R_(a)=81 and R₉=24respectively, the scores of the color rendering indices can be improvedto R_(a)=98 and R₉=95 when a red source is included (refer to PatentDocument 2).

In addition, another attempt involves adjusting a spectrum emitted froma light-emitting device particularly for special illuminationapplications so that color appearance of an object is based on a desiredcolor. For example, Non-Patent Document 1 describes a red-basedillumination light source.

-   Patent Document 1: Japanese Patent Publication No. 3503139-   Patent Document 2: WO2011/024818-   Non-Patent Document 1: General-purpose fluorescent light Meat-kun,    [online], Prince Electric Co., LTD., [retrieved on May 16, 2011],    Internet <URL:    http://www.prince-d.co.jp/pdct/docs/pdf/catalog_pdf/fl_nrb_ca2    011.pdf>-   Non-Patent Document 2: LEDs MAGAZINE, [retrieved on Aug. 22, 2011],    Internet <URL: http://www.ledsmagazine.com/news/8/8/2>

A color rendering index is an index which indicates how close a colorappearance is, when illuminating with light (test light) of alight-emitting device that is an evaluation object, compared to a colorappearance when illuminating with a “reference light” that is selectedin correspondence with a CCT of the test light. In other words, a colorrendering index is an index indicating fidelity of the light-emittingdevice that is an evaluation object. However, recent studies have madeit increasingly clear that a high average color rendering index (R_(a))or a high special color rendering index (R_(i) (where i ranges from 1 to14 or, in Japan, ranges from 1 to 15 pursuant to JIS) does notnecessarily lead to favorable color perception in a person. In otherwords, there is a problem that the aforementioned methods for improvingcolor rendering index scores do not always achieve favorable colorappearance.

Furthermore, the effect of illuminance of an illuminated object causinga variation in color appearance is not included in various colorrendition metric that are currently in use. It is an everyday experiencethat a vivid color of a flower seen outdoors where illuminance isnormally around 10000 lx or higher becomes dull once the flower isbrought indoors where illuminance is around 500 lx as though the floweritself has changed to a different flower with lower chroma, even thoughthe color is fundamentally the same. Generally, saturation regarding thecolor appearance of an object is dependent on illuminance, andsaturation decreases as illuminance decreases even though a spectralpower distribution that is being illuminated is unchanged. In otherwords, color appearance becomes dull. This effect is known as the Hunteffect.

Despite having a significant effect on color rendering property, asthings stand, the Hunt effect is not actively considered for overallevaluation of a light-emitting device such as a light source, a fixture,or a system. In addition, while the simplest way to compensate for theHunt effect is to dramatically increase indoor illuminance, this causesan unnecessary increase in energy consumption. Furthermore, a specificmethod of achieving a color appearance or an object appearance that isas natural, vivid, highly visible, and comfortable as perceived outdoorsunder illuminance comparable to an indoor illumination environmentremains to be revealed.

Meanwhile, with light having its spectrum adjusted so as to, forexample, increase chroma of red to be used for special illumination inrestaurants or for food illumination, there is a problem that hue(angle) deviation increases in comparison to reference light asevidenced by yellow appearing reddish or blue appearing greenish. Inother words, the color appearance of colors other than a specific colorof an illuminated object becomes unnatural. Another problem is that whena white object is illuminated by such light, the white object itselfappears colored and is no longer perceived as being white.

DISCLOSURE OF THE INVENTION

The present invention has been made in order to solve problems such asthose described above, and a primary object of the present invention isto provide an illumination method and an overall light-emitting devicesuch as an illumination light source, a lighting fixture, and a lightingsystem which are capable of achieving, under an indoor illuminationenvironment where illuminance is around 5000 lx or lower including caseswhere detailed work is performed and generally around 1500 lx or lower,a color appearance or an object appearance as perceived by a personwhich is as natural, vivid, highly visible, and comfortable as perceivedoutdoors in a high-illuminance environment regardless of scores ofvarious color rendition metric. Another object of the present inventionis to achieve a highly efficient and comfortable illuminatedenvironment. Yet another object of the present invention is to provide adesign guideline for such favorable light-emitting devices.

In order to achieve the objects described above, a first embodiment ofthe present invention relates to the following.

[1] An illumination method comprising: illuminated objects preparationstep of preparing illuminated objects; and an illumination step ofilluminating the objects by light emitted from light-emitting devicesincluding a semiconductor light-emitting element that is alight-emitting element, wherein

in the illumination step, when light emitted from the light-emittingdevices illuminate the objects, the objects are illuminated so that thelight measured at a position of the objects satisfies (1), (2), and (3)below:

(1) a distance D_(uvSSL) from a black-body radiation locus as defined byANSI C78.377 of the light measured at the position of the objectssatisfies −0.0350≤D_(uvSSL)≤−0.0040;(2) if an a* value and a b* value in CIE 1976 L*a*b* color space of 15Munsell renotation color samples from #01 to #15 listed below whenmathematically assuming illumination by the light measured at theposition of the objects are respectively denoted by a*_(nSSL) andb*_(nSSL) (where n is a natural number from 1 to 15), and

if an a* value and a b* value in CIE 1976 L*a*b* color space of the 15Munsell renotation color samples when mathematically assumingillumination by a reference light that is selected according to acorrelated color temperature T_(SSL) (K) of the light measured at theposition of the objects are respectively denoted by a*_(nref) andb*_(nref) (where n is a natural number from 1 to 15), then eachsaturation difference ΔC_(n) satisfies

−3.8≤ΔC _(n)≤18.6 (where n is a natural number from 1 to 15),

an average saturation difference represented by formula (1) belowsatisfies formula (2) below and

$\begin{matrix}\left\lbrack {{Expression}\mspace{14mu} 1} \right\rbrack & \; \\\frac{\sum\limits_{n = 1}^{15}{\Delta \; C_{n}}}{15} & (1) \\\left\lbrack {{Expression}\mspace{14mu} 2} \right\rbrack & \; \\{1.0 \leqq \frac{\sum\limits_{n = 1}^{15}{\Delta \; C_{n}}}{15} \leqq 7.0} & (2)\end{matrix}$

if a maximum saturation difference value is denoted by ΔC_(max) and aminimum saturation difference value is denoted by ΔC_(min), then adifference |ΔC_(max)−ΔC_(min)| between the maximum saturation differencevalue and the minimum saturation difference value satisfies

2.8≤(|ΔC _(max) −ΔC _(min)|)≤19.6,

where ΔC _(n)=√{(a* _(nSSL))²+(b* _(nSSL))²}−√{(a* _(nref))²+(b*_(nref))²}

with the 15 Munsell renotation color samples being:

#01 7.5P 4/10

#02 10PB 4/10

#03 5PB 4/12

#04 7.5B 5/10

#05 10BG 6/8

#06 2.5BG 6/10

#07 2.5G 6/12

#08 7.5GY 7/10

#09 2.5GY 8/10

#10 5Y 8.5/12

#11 10YR 7/12

#12 5YR 7/12

#13 10R 6/12

#14 5R 4/14

#15 7.5RP 4/12

(3) if hue angles in CIE 1976 L*a*b* color space of the 15 Munsellrenotation color samples when mathematically assuming illumination bythe light measured at the position of the objects are denoted byθ_(nSSL) (degrees) (where n is a natural number from 1 to 15), and

if hue angle in CIE 1976 L*a*b* color space of the 15 Munsell renotationcolor samples when mathematically assuming illumination by a referencelight that is selected according to the correlated color temperatureT_(SSL) (K) of the light measured at the position of the objects aredenoted by θ_(nref) (degrees) (where n is a natural number from 1 to15), then an absolute value of each difference in hue angles |Δh_(n)|satisfies

0≤|Δh _(n)|≤9.0 (degrees) (where n is a natural number from 1 to 15),

where Δh_(n)=θ_(nSSL)−θ_(nref).[2] The illumination method according to [1], wherein

if a spectral power distribution of the light measured at the positionof the objects is denoted by ϕ_(SSL)(λ), a spectral power distributionof the reference light that is selected according to T_(SSL) (K) of thelight measured at the position of the objects is denoted by ϕ_(ref)(λ),tristimulus values of the light measured at the position of the objectsare denoted by (X_(SSL), Y_(SSL), Z_(SSL)), and tristimulus values ofthe reference light that is selected according to T_(SSL) (K) of thelight measured at the position of the object are denoted by (X_(ref),Y_(ref), Z_(ref)), a normalized spectral power distribution S_(SSL)(λ)of the light measured at the position of the objects, a normalizedspectral power distribution S_(ref)(λ) of the reference light that isselected according to T_(SSL) (K) of the light measured at the positionof the object, and a difference ΔS (λ) between the normalized spectralpower distributions are respectively defined as

S _(SSL)(λ)=ϕ_(SSL)(λ)/Y _(SSL),

S _(ref)(λ)=ϕ_(ref)(λ)/Y _(ref) and

ΔS(λ)=S _(ref)(λ)−S _(SSL)(λ), and

a wavelength that produces a longest wavelength local maximum value ofS_(SSL)(λ) in a wavelength range from 380 nm to 780 nm is denoted byλ_(R) (nm), then a wavelength Λ4 that assumes S_(SSL)(λ_(R))/2 exists ona longer wavelength-side of λ_(R), and

an index A_(cg) represented by formula (3) below of the light measuredat the position of the objects satisfies −360≤A_(cg)≤−10

[Expression 3]

A _(cg)=∫₃₈₀ ⁴⁹⁵ ΔS(λ)dλ+∫ ₄₉₅ ⁵⁹⁰(−ΔS(λ))dλ+∫ ₅₉₀ ^(Λ4) ΔS(λ)dλ  (3).

[3] The illumination method according to [1], wherein

if a spectral power distribution of light measured at the position ofthe object is denoted by ϕ_(SSL)(λ), a spectral power distribution ofthe reference light that is selected according to T_(SSL) (K) of thelight measured at the position of the objects is denoted by ϕ_(ref)(λ),tristimulus values of the light measured at the position of the objectsare denoted by (X_(SSL), Y_(SSL), Z_(SSL)), and tristimulus values ofthe reference light that is selected according to T_(SSL) (K) of thelight measured at the position of the objects are denoted by (X_(ref),Y_(ref), Z_(ref)), and

if a normalized spectral power distribution S_(SSL)(λ) of the lightmeasured at the position of the objects, a normalized spectral powerdistribution S_(ref)(λ) of the reference light that is selectedaccording to T_(SSL) (K) of the light measured at the position of theobjects, and a difference ΔS (λ) between the normalized spectral powerdistributions are respectively defined as

S _(SSL)(λ)=ϕ_(SSL)(λ)/Y _(SSL),

S _(ref)(λ)=ϕ_(ref)(λ)/Y _(ref) and

ΔS(λ)=S _(ref)(λ)−S _(SSL)(λ) and moreover

a wavelength that produces a longest wavelength local maximum value ofS_(SSL)(λ) in a wavelength range from 380 nm to 780 nm is denoted byλ_(R) (nm), then a wavelength Λ4 that assumes S_(SSL)(λ_(R))/2 does notexist on a longer wavelength-side of λ_(R), and

an index A_(cg) represented by formula (4) below of the light measuredat the position of the object satisfies −360≤A_(cg)≤−10

[Expression 4]

A _(cg)=∫₃₈₀ ⁴⁹⁵ ΔS(λ)dλ+∫ ₄₉₅ ⁵⁹⁰(−ΔS(λ))dλ+∫ ₅₉₀ ^(Λ4) ΔS(λ)dλ  (4).

[4] The illumination method according to any one of [1] to [3], wherein

a luminous efficacy of radiation K (lm/W) in a wavelength range from 380nm 780 nm as derived from the spectral power distribution ϕ_(SSL)(λ) oflight measured at the position of the object satisfies

180 (lm/W)≤K (lm/W)≤320 (lm/W).

[5] The illumination method according to any one of [1] to [4], whereineach of the absolute value of the difference in hue angles |Δh_(n)|satisfies

0.003≤|Δh _(n)|≤8.3 (degrees) (where n is a natural number from 1 to15).

[6] The illumination method according to any one of [1] to [5], whereinthe average saturation difference represented by the general formula (1)satisfies formula (2)′ below

$\begin{matrix}\left\lbrack {{Expression}\mspace{14mu} 5} \right\rbrack & \; \\{1.2 \leqq \frac{\sum\limits_{n = 1}^{15}{\Delta \; C_{n}}}{15} \leqq {6.3.}} & (2)^{\prime}\end{matrix}$

[7] The illumination method according to any one of [1] to [6], whereineach of the saturation difference ΔC_(n) satisfies

−3.4≤ΔC _(n)≤16.8 (where n is a natural number from 1 to 15).

[8] The illumination method according to any one of [1] to [7], whereinthe difference |ΔC_(max)−ΔC_(min)| between the maximum saturationdifference value and the minimum saturation difference value satisfies

3.2≤(|ΔC _(max) −ΔC _(min)|)≤17.8.

[9] The illumination method according to any one of [1] to [8], wherein

the distance D_(uvSSL) from a black-body radiation locus of the lightmeasured at the position of the objects satisfies

−0.0250≤D _(uvSSL)≤−0.0100.

[10] The illumination method according to [2] or [3], wherein the indexA_(cg) represented by the formula (3) or (4) satisfies

−322≤A _(cg)≤−12.

[11] The illumination method according to any one of [1] to [10],wherein

the luminous efficacy of radiation K (lm/W) in a wavelength range from380 nm to 780 nm as derived from the spectral power distributionϕ_(SSL)(λ) of the light measured at the position of the object satisfies

206 (lm/W)≤K (lm/W)≤288 (lm/W).

[12] The illumination method according to any one of [1] to [11],wherein the correlated color temperature T_(SSL) (K) of the lightmeasured at the position of the objects satisfies

2550 (K)≤T _(SSL) (K)≤5650 (K)

[13] The illumination method according to any one of [1] to [12],wherein illuminance at which the objects are illuminated is 150 lx to5000 lx.[14] The illumination method according to any one of [1] to [13],wherein the light-emitting devices emit light emitted from one to sixlight-emitting elements including the light emitted by the semiconductorlight-emitting element.[15] The illumination method according to any one of [1] to [14],wherein the peak wavelength of the emission spectrum of thesemiconductor light-emitting element is 380 nm or longer and shorterthan 495 nm and the full-width at half-maximum of the emission spectrumof the semiconductor light-emitting element is from 2 nm to 45 nm.[16] The illumination method according to [15], wherein the peakwavelength of the emission spectrum of the semiconductor light-emittingelement is 395 nm or longer and shorter than 420 nm.[17] The illumination method according to [15], wherein the peakwavelength of the emission spectrum of the semiconductor light-emittingelement is 420 nm or longer and shorter than 455 nm.[18] The illumination method according to [15], wherein the peakwavelength of the emission spectrum of the semiconductor light-emittingelement is 455 nm or longer and shorter than 485 nm.[19] The illumination method according to any one of [1] to [14],wherein the peak wavelength of the emission spectrum of thesemiconductor light-emitting element is 495 nm or longer and shorterthan 590 nm and the full-width at half-maximum of the emission spectrumof the semiconductor light-emitting element is 2 nm to 75 nm.[20] The illumination method according to any one of [1] to [14],wherein the peak wavelength of the emission spectrum of thesemiconductor light-emitting element is 590 nm or longer and shorterthan 780 nm and the full-width at half-maximum of the emission spectrumof the semiconductor light-emitting element is 2 nm to 30 nm.[21] The illumination method according to any one of [1] to [20],wherein the semiconductor light-emitting element is created on anysubstrate selected from the group consisting of a sapphire substrate, aGaN substrate, a GaAs substrate, and a GaP substrate.[22] The illumination method according to any one of [1] to [20],wherein the semiconductor light-emitting element is fabricated on a GaNsubstrate or a GaP substrate and a thickness of the substrate is 100 μmto 2 mm.[23] The illumination method according to any one of [1] to [20],wherein the semiconductor light-emitting element is fabricated on asapphire substrate or a GaAs substrate and the semiconductorlight-emitting element is detached removed from the substrate.[24] The illumination method according to any one of [1] to [23],comprising a phosphor as a light-emitting element.[25] The illumination method according to [24], wherein the phosphorincludes one to five phosphors each having different emission spectra.[26] The illumination method according to [24] or [25], wherein thephosphor includes a phosphor having an individual emission spectrum,when photoexcited at room temperature, with a peak wavelength of 380 nmor longer and shorter than 495 nm and a full-width at half-maximum of 2nm to 90 nm.[27] The illumination method according to [26], wherein the phosphorincludes one or more types of phosphors selected from the groupconsisting of a phosphor represented by general formula (5) below, aphosphor represented by general formula (5)′ below, (Sr,Ba)₃MgSi₂O₈:Eu²⁺, and (Ba,Sr,Ca, Mg)Si₂O₂N₂: Eu

(Ba,Sr,Ca)MgAl₁₀O₁₇: Mn,Eu  (5)

Sr_(a)Ba_(b)Eu_(x)(PO₄)_(c)X_(d)  (5)′

(in the general formula (5)′, X is Cl, in addition, c, d, and x arenumbers satisfying 2.7≤c≤3.3, 0.9≤d≤1.1, and 0.3≤x≤1.2, moreover, a andb satisfy conditions represented by a+b=5−x and 0≤b/(a+b)≤0.6).[28] The illumination method according to [24] or [25], wherein thephosphor includes a phosphor having an individual emission spectrum,when photoexcited at room temperature, with a peak wavelength of 495 nmor longer and shorter than 590 nm and a full-width at half-maximum of 2nm to 130 nm.[29] The illumination method according to [28], wherein the phosphorincludes one or more types of phosphors selected from the groupconsisting of Si_(6-z)Al_(z)O_(z)N_(8-z):Eu (where 0<z<4.2), a phosphorrepresented by general formula (6) below, a phosphor represented bygeneral formula (6)′ below, and SrGaS₄:Eu²⁺

(Ba_(a)Ca_(b)Sr_(c)Mg_(d)Eu_(x))SiO₄  (6)

(In the general formula (6), a, b, c, d and x satisfy a+b+c+d+x=2,1.0≤a≤2.0, 0≤b<0.2, 0.2≤c≤0.8, 0≤d<0.2, and 0<x≤0.5)

Ba_(1-x-y)Sr_(x)Eu_(y)Mg_(1-z)Mn_(z)Al₁₀O₁₇  (6)′

(In general formula (6)′, x, y, and z respectively satisfy 0.1≤x≤0.4,0.25≤y≤0.6, and 0.05≤z≤0.5).[30] The illumination method according to [24] or [25], wherein thephosphor includes a phosphor having an individual emission spectrum,when photoexcited at room temperature, with a peak wavelength of 590 nmor longer and shorter than 780 nm and a full-width at half-maximum of 2nm to 130 nm.[31] The illumination method according to [30], wherein the phosphorincludes one or more types of phosphors selected from the groupconsisting of a phosphor represented by general formula (7) below, aphosphor represented by general formula (7)′ below, (Sr,Ca,Ba)₂Al_(x)Si_(5-x)O_(x)N_(8-x): Eu (where 0≤x≤2), Eu_(y)(Sr,Ca,Ba)_(1-y):Al_(1+x)Si_(4-x)O_(x)N_(7-x) (where 0≤x<4, 0≤y<0.2),K₂SiF₆:Mn⁴⁺, A_(2+x)M_(y)Mn_(z)Fn (where A is Na and/or K; M is Si andAl; −1≤x≤1 and 0.9≤y+z≤1.1 and 0.001≤z≤0.4 and 5≤n≤7), (Ca, Sr,Ba, Mg)AlSiN₃:Eu and/or (Ca, Sr, Ba)AlSiN₃:Eu, and(CaAlSiN₃)_(1-x)(Si₂N₂O)_(x):Eu (where x satisfies 0<x<0.5)

(La_(1-x-y),Eu_(x),Ln_(y))₂O₂S  (7)

(in the general formula (7), x and y denote numbers respectivelysatisfying 0.02≤x≤0.50 and 0≤y≤0.50, and Ln denotes at least onetrivalent rare-earth element among Y, Gd, Lu, Sc, Sm, and Er)

(k−x)MgO.xAF₂.GeO₂ :yMn⁴⁺  (7)′

(in the general formula (7)′, k, x, and y denote numbers respectivelysatisfying 2.8≤k≤5, 0.1≤x≤0.7, and 0.005≤y≤0.015, and A is calcium (Ca),strontium (Sr), barium (Ba), zinc (Zn), or a mixture consisting of theseelements).[32] The illumination method according to any one of [1] to [14]comprising a phosphor as a light-emitting element, wherein a peakwavelength of an emission spectrum of the semiconductor light-emittingelement is 395 nm or longer and shorter than 420 nm, and the phosphorincludes SBCA, β-SiAlON, and CASON.[33] The illumination method according to any one of [1] to [14]comprising a phosphor as a light-emitting element, wherein a peakwavelength of an emission spectrum of the semiconductor light-emittingelement is 395 nm or longer and shorter than 420 nm, and the phosphorincludes SCA, β-SiAlON, and CASON.[34] The illumination method according to any one of [1] to [33],wherein the light-emitting device is any one selected from the groupconsisting of a packaged LED, an LED module, an LED lighting fixture,and an LED lighting system.[35] The illumination method according to any one of [1] to [34], whichis for residential uses.[36] The illumination method according to any one of [1] to [34], whichis used for exhibition uses.[37] The illumination method according to any one of [1] to [34], whichis used for presentation purposes.[38] The illumination method according to any one of [1] to [34], whichis used for medical uses.[39] The illumination method according to any one of [1] to [34], whichis for work use.[40] The illumination method according to any one of [1] to [34], whichis used inside industrial devices.[41] The illumination method according to any one of [1] to [34], whichis used in interior of public transportation.[42] The illumination method according to any one of [1] to [34], whichis used for works of art.[43] The illumination method according to any one of [1] to [34], whichis used for aged persons.[44] A light-emitting device comprising at least a semiconductorlight-emitting element as a light-emitting element, wherein

light emitted from the light-emitting device includes, in a main radiantdirection thereof, light whose distance D_(uvSSL) from a black-bodyradiation locus as defined by ANSI C78.377 satisfies

−0.0350≤D _(uvSSL)≤−0.0040, and

if a spectral power distribution of light emitted from thelight-emitting device in the radiant direction is denoted by ϕ_(SSL)(λ),a spectral power distribution of a reference light that is selectedaccording to T_(SSL) (K) of the light emitted from the light-emittingdevice in the radiant direction is denoted by ϕ_(ref)(λ), tristimulusvalues of the light emitted from the light-emitting device in theradiant direction are denoted by (X_(SSL), Y_(SSL), Z_(SSL)), andtristimulus values of the reference light that is selected according toT_(SSL) (K) of the light emitted from the light-emitting device in theradiant direction are denoted by (X_(ref), Y_(ref), Z_(ref)), and

if a normalized spectral power distribution S_(SSL)(λ) of light emittedfrom the light-emitting device in the radiant direction, a normalizedspectral power distribution Sr_(ef)(λ) of a reference light that isselected according to T_(SSL) (K) of the light emitted from thelight-emitting device in the radiant direction, and a difference ΔS (λ)between these normalized spectral power distributions are respectivelydefined as

S _(SSL)(λ)=ϕ_(SSL)(λ)/Y _(SSL),

S _(ref)(λ)=ϕ_(ref)(λ)/Y _(ref) and

ΔS(λ)=S _(ref)(λ)−S _(SSL)(λ) and

a wavelength that produces a longest wavelength local maximum value ofS_(SSL)(λ) in a wavelength range of 380 nm to 780 nm is denoted by λ_(R)(nm), then a wavelength Λ4 that assumes S_(SSL)(λ_(R))/2 exists on alonger wavelength-side of λ_(R), and

an index A_(cg) represented by formula (3) below satisfies−360≤A_(cg)≤−10

[Expression 6]

A _(cg)=∫₃₈₀ ⁴⁹⁵ ΔS(λ)dλ+∫ ₄₉₅ ⁵⁹⁰(−ΔS(λ))dλ+∫ ₅₉₀ ^(Λ4) ΔS(λ)dλ  (3).

[45] A light-emitting device comprising at least a semiconductorlight-emitting element as a light-emitting element, wherein

light emitted from the light-emitting device includes, in a main radiantdirection thereof, light whose distance D_(uvSSL) from a black-bodyradiation locus as defined by ANSI C78.377 satisfies−0.0350≤D_(uvSSL)≤−0.0040, and

if a spectral power distribution of light emitted from thelight-emitting device in the radiant direction is denoted by ϕ_(SSL)(λ),a spectral power distribution of a reference light that is selectedaccording to T_(SSL) (K) of the light emitted from the light-emittingdevice in the radiant direction is denoted by ϕ_(ref)(λ), tristimulusvalues of the light emitted from the light-emitting device in theradiant direction are denoted by (X_(SSL), Y_(SSL), Z_(SSL)), andtristimulus values of the reference light that is selected according toT_(SSL) (K) of the light emitted from the light-emitting device in theradiant direction are denoted by (X_(ref), Y_(ref), Z_(ref)), and

if a normalized spectral power distribution S_(SSL)(λ) of light emittedfrom the light-emitting device in the radiant direction, a normalizedspectral power distribution S_(ref)(λ) of reference light that isselected according to T_(SSL) (K) of the light emitted from thelight-emitting device in the radiant direction, and a difference ΔS (λ)between these normalized spectral power distributions are respectivelydefined as

S _(SSL)(λ)=ϕ_(SSL)(λ)/Y _(SSL),

S _(ref)(λ)=ϕ_(ref)(λ)/Y _(ref) and

ΔS(λ)=S _(ref)(λ)−S _(SSL)(λ), and

a wavelength that produces a longest wavelength local maximum value ofS_(SSL)(λ) in a wavelength range of 380 nm to 780 nm is denoted by λ_(R)(nm), then a wavelength Λ4 that assumes S_(SSL)(λ_(R))/2 does not existon a longer wavelength-side of λ_(R), and

an index A_(cg) represented by formula (4) below satisfies−360≤A_(cg)≤−10

[Expression 7]

A _(cg)=∫₃₈₀ ⁴⁹⁵ ΔS(λ)dλ+∫ ₄₉₅ ⁵⁹⁰(−ΔS(λ))dλ+∫ ₅₉₀ ^(Λ4) ΔS(λ)dλ  (4).

[46] The light-emitting device according to [44] or [45], wherein

the light emitted from the light-emitting device in the radiantdirection satisfies (1) and (2) below:

(1) if an a* value and a b* value in CIE 1976 L*a*b* color space of 15Munsell renotation color samples from #01 to #15 listed below whenmathematically assuming illumination by the light emitted from thelight-emitting device in the radiant direction are respectively denotedby a*n_(SSL) and b*_(nSSL) (where n is a natural number from 1 to 15),and

an a* value and a b* value in CIE 1976 L*a*b* color space of the 15Munsell renotation color samples when mathematically assumingillumination by a reference light that is selected according to acorrelated color temperature T_(SSL) (K) of the light emitted from thelight-emitting device in the radiant direction are respectively denotedby a*_(nref) and b*_(nref) (where n is a natural number from 1 to 15),then each saturation difference ΔC_(n) satisfies

−3.8≤ΔC _(n)≤18.6 (where n is a natural number from 1 to 15),

an average saturation difference represented by formula (1) belowsatisfies formula (2) below and

$\begin{matrix}\left\lbrack {{Expression}\mspace{14mu} 8} \right\rbrack & \; \\\frac{\sum\limits_{n - 1}^{15}{\Delta \; C_{n}}}{15} & (1) \\\left\lbrack {{Expression}\mspace{14mu} 9} \right\rbrack & \; \\{1.0 \leqq \frac{\sum\limits_{n = 1}^{15}{\Delta \; C_{n}}}{15} \leqq 7.0} & (2)\end{matrix}$

andif a maximum saturation difference value is denoted by ΔC_(max) and aminimum saturation difference value is denoted by ΔC_(min), then adifference |ΔC_(max)−ΔC_(min)| between the maximum saturation differencevalue and the minimum saturation difference value satisfies

2.8≤(|ΔC _(max) −ΔC _(min)|)−19.6,

where ΔC_(n)=√{(a*_(nSSL))²+(b*_(nSSL))²}−√{(a*_(nref))²+(b*_(nref))²}

with the 15 Munsell renotation color samples being:

#01 7.5P 4/10

#02 10PB 4/10

#03 5PB 4/12

#04 7.5B 5/10

#05 10BG 6/8

#06 2.5BG 6/10

#07 2.5G 6/12

#08 7.5GY 7/10

#09 2.5GY 8/10

#10 5Y 8.5/12

#11 10YR 7/12

#12 5YR 7/12

#13 10R 6/12

#14 5R 4/14

#15 7.5RP 4/12

(2) if hue angles in a CIE 1976 L*a*b* color space of the 15 Munsellrenotation color samples when mathematically assuming illumination bythe light emitted from the light-emitting device in the radiantdirection is denoted by θ_(nSSL) (degrees) (where n is a natural numberfrom 1 to 15), and

hue angles in a CIE 1976 L*a*b* color space of the 15 Munsell renotationcolor samples when mathematically assuming illumination by a referencelight that is selected according to the correlated color temperatureT_(SSL) (K) of the light emitted in the radiant direction are denoted byθ_(nref) (degrees) (where n is a natural number from 1 to 15), then anabsolute value of each difference in hue angles |Δh_(n)| satisfies

0≤|Δh _(n)|≤9.0 (degrees) (where n is a natural number from 1 to 15),

where Δh_(n)=θ_(nSSL)−θ_(nref).[47] The light-emitting device according to any one of [44] to [46],wherein

a luminous efficacy of radiation K (lm/W) in a wavelength range from 380nm to 780 nm as derived from the spectral power distribution ϕ_(SSL)(λ)of light emitted from the light-emitting device in the radiant directionsatisfies

180 (lm/W)≤K (lm/W)≤320 (lm/W).

[48] The light-emitting device according to [46], wherein each of theabsolute value of the difference in hue angles |Δh_(n)| satisfies

0.003≤|Δh _(n)|≤8.3 (degrees) (where n is a natural number from 1 to15).

[49] The light-emitting device according to [46], wherein the averagesaturation difference represented by the general formula (1) abovesatisfies formula (2)′ below

$\begin{matrix}\left\lbrack {{Expression}\mspace{14mu} 10} \right\rbrack & \; \\{1.2 \leqq \frac{\sum\limits_{n = 1}^{15}{\Delta \; C_{n}}}{15} \leqq {6.3.}} & (2)^{\prime}\end{matrix}$

[50] The light-emitting device according to [46], wherein each of thesaturation difference ΔC_(n) satisfies

−3.4≤ΔC _(n)≤16.8 (where n is a natural number from 1 to 15).

[51] The light-emitting device according to [46], wherein the difference_(n)|ΔC_(max)−ΔC_(min)| between the maximum saturation difference valueand the minimum saturation difference value satisfies

3.2≤(|ΔC _(max) −ΔC _(min)|)≤17.8.

[52] The light-emitting device according to any one of [44] to [51],wherein

a distance D_(uvSSL) from a black-body radiation locus of the lightemitted from the light-emitting device in the radiant directionsatisfies

−0.0250≤D _(uvSSL)≤−0.0100.

[53] The light-emitting device according to any one of [44] to [52],wherein the index A_(cg) represented by the formula (3) or (4) abovesatisfies

−322≤A _(cg)≤−12.

[54] The light-emitting device according to any one of [44] to [53],wherein

the luminous efficacy of radiation K (lm/W) in a wavelength range from380 nm to 780 nm as derived from the spectral power distributionϕ_(SSL)(λ) of light emitted from the light-emitting device in theradiant direction satisfies

206 (lm/W)≤K (lm/W)≤288 (lm/W).

[55] The light-emitting device according to any one of [44] to [54],wherein the correlated color temperature T_(SSL) (K) satisfies

2550 (K)≤T _(SSL) (K)≤5650 (K).

[56] The light-emitting device according to any one of [44] to [55],wherein illuminance at which the light emitted from the light-emittingdevice in the radiant direction illuminates objects is 150 lx to 5000lx.[57] The light-emitting device according to any one of [44] to [56],wherein the light-emitting device emits, in the radiant direction, lightemitted from one to six light-emitting elements including the lightemitted by the semiconductor light-emitting element.[58] The light-emitting device according to any one of [44] to [57],wherein a peak wavelength of an emission spectrum of the semiconductorlight-emitting element is 380 nm or longer and shorter than 495 nm andthe full-width at half-maximum of the emission spectrum of thesemiconductor light-emitting element is 2 nm to 45 nm.[59] The light-emitting device according to [58], wherein the peakwavelength of the emission spectrum of the semiconductor light-emittingelement is 395 nm or longer and shorter than 420 nm.[60] The light-emitting device according to [58], wherein the peakwavelength of the emission spectrum of the semiconductor light-emittingelement is 420 nm or longer and shorter than 455 nm.[61] The light-emitting device according to [58], wherein the peakwavelength of the emission spectrum of the semiconductor light-emittingelement is 455 nm or longer and shorter than 485 nm.[62] The light-emitting device according to any one of [44] to [57],wherein the peak wavelength of the emission spectrum of thesemiconductor light-emitting element is 495 nm or longer and shorterthan 590 nm and the full-width at half-maximum of the emission spectrumof the semiconductor light-emitting element is 2 nm to 75 nm.[63] The light-emitting device according to any one of [44] to [57],wherein the peak wavelength of the emission spectrum of thesemiconductor light-emitting element is 590 nm or longer and shorterthan 780 nm and the full-width at half-maximum of the emission spectrumof the semiconductor light-emitting element is 2 nm to 30 nm.[64] The light-emitting device according to any one of [44] to [63],wherein the semiconductor light-emitting element is fabricated on anysubstrate selected from the group consisting of a sapphire substrate, aGaN substrate, a GaAs substrate, and a GaP substrate.[65] The light-emitting device according to any one of [44] to [63],wherein the semiconductor light-emitting element is fabricated on a GaNsubstrate or a GaP substrate and a thickness of the substrate is 100 mto 2 mm.[66] The light-emitting device according to any one of [44] to [63],wherein the semiconductor light-emitting element is fabricated on asapphire substrate or a GaAs substrate and the semiconductorlight-emitting element is removed from the substrate.[67] The light-emitting device according to any one of [44] to [66],comprising a phosphor as a light-emitting element.[68] The light-emitting device according to [67], wherein the phosphorincludes one to five phosphors each having different emission spectra.[69] The light-emitting device according to [67] or [68], wherein thephosphor includes a phosphor having an individual emission spectrum,when photoexcited at room temperature, with a peak wavelength of 380 nmor longer and shorter than 495 nm and a full-width at half-maximum of 2nm to 90 nm.[70] The light-emitting device according to [69], wherein the phosphorincludes one or more types of phosphors selected from the groupconsisting of a phosphor represented by general formula (5) below, aphosphor represented by general formula (5)′ below, (Sr, Ba)₃MgSi₂O₈:Eu²⁺, and (Ba,Sr,Ca, Mg) Si₂O₂N₂: Eu

(Ba,Sr,Ca)MgAl₁₀O₁₇:Mn,Eu  (5)

Sr_(a)Ba_(b)Eu_(x)(PO₄)_(c)X_(d)  (5)′

(in the general formula (5)′, X is Cl, in addition, c, d, and x arenumbers satisfying 2.7≤c≤3.3, 0.9≤d≤1.1, and 0.3≤x≤1.2, moreover, a andb satisfy conditions represented by a+b=5−x and 0≤b/(a+b)≤0.6).[71] The light-emitting device according to [67] or [68], wherein thephosphor includes a phosphor having an individual emission spectrum,when photoexcited at room temperature, with a peak wavelength of 495 nmor longer and shorter than 590 nm and a full-width at half-maximum of 2nm to 130 nm.[72] The light-emitting device according to [71], wherein the phosphorincludes one or more types of phosphors selected from the groupconsisting of Si_(6-z)Al_(z)O_(z)N_(8-z):Eu (where 0<z<4.2), a phosphorrepresented by general formula (6) below, a phosphor represented bygeneral formula (6)′ below, and SrGaS₄:Eu²⁺

(Ba_(a)Ca_(b)Sr_(c)Mg_(d)Eu_(x)) SiO₄  (6)

(in the general formula (6), a, b, c, d, and x satisfy a+b+c+d+x=2,1.0≤a≤2.0, 0≤b<0.2, 0.2≤c≤0.8, 0≤d<0.2, and 0<x≤0.5).

Ba_(1-x-y)Sr_(x)Eu_(y)Mg_(1-z)Mn_(z)Al₁₀O₁₇  (6)′

(in the general formula (6)′, x, y, and z respectively satisfy0.1≤x≤0.4, 0.25≤y≤0.6, and 0.05≤z≤0.5).[73] The light-emitting device according to [67] or [68], wherein thephosphor includes a phosphor having an individual emission spectrum,when photoexcited at room temperature, with a peak wavelength of 590 nmor longer and shorter than 780 nm and a full-width at half-maximum of 2nm to 130 nm.[74] The light-emitting device according to [73], wherein the phosphorincludes one or more types of phosphors selected from the groupconsisting of a phosphor represented by general formula (7) below, aphosphor represented by general formula (7)′ below, (Sr,Ca,Ba)₂Al_(x)Si_(5-x)O_(x)N_(8-x): Eu (where 0≤x≤2),Eu_(y)(Sr,Ca,Ba)_(1-y):Al_(1+x)Si_(4-x)O_(x)N_(7-x) (where 0≤x<4,0≤y<0.2), K₂SiF₆:Mn⁴⁺, A_(2+x)M_(y)Mn_(z)F_(n) (where A is Na and/or K;M is Si and Al; −1≤x≤1 and 0.9≤y+z≤1.1 and 0.001≤z≤0.4 and 5≤n≤7),(Ca,Sr,Ba,Mg)AlSiN₃:Eu and/or (Ca,Sr,Ba)AlSiN₃:Eu, and(CaAlSiN₃)_(1-x)(Si₂N₂O)_(x):Eu (where x satisfies 0<x<0.5)

(La_(1-x-y),Eu_(x),Ln_(y))₂O₂S  (7)

(in the general formula (7), x and y denote numbers respectivelysatisfying 0.02≤x≤0.50 and 0≤y≤0.50, and Ln denotes at least onetrivalent rare-earth element among Y, Gd, Lu, Sc, Sm, and Er)

(k−x)MgO.xAF₂.GeO₂ :yMn⁴⁺  (7)′

(in the general formula (7)′, k, x, and y denote numbers respectivelysatisfying 2.8≤k≤5, 0.1≤x≤0.7, and 0.005≤y≤0.015, and A is calcium (Ca),strontium (Sr), barium (Ba), zinc (Zn), or a mixture consisting of theseelements).[75] The light-emitting device according to any one of [44] to [57]comprising a phosphor as a light-emitting element, wherein a peakwavelength of an emission spectrum of the semiconductor light-emittingelement is 395 nm or longer and shorter than 420 nm, and the phosphorincludes SBCA, β-SiAlON, and CASON.[76] The light-emitting device according to any one of [44] to [57]comprising a phosphor as a light-emitting element, wherein a peakwavelength of an emission spectrum of the semiconductor light-emittingelement is 395 nm or longer and shorter than 420 nm, and the phosphorincludes SCA, β-SiAlON, and CASON.[77] The light-emitting device according to any one of [44] to [76],which is selected from the group consisting of a packaged LED, an LEDmodule, an LED lighting fixture, and an LED lighting system.[78] The light-emitting device according to any one of [44] to [77],which is used as a residential uses' device.[79] The light-emitting device according to any one of [44] to [77],which is used as a exhibition illumination device.[80] The light-emitting device according to any one of [44] to [77],which is used as a presentation illumination device.[81] The light-emitting device according to any one of [44] to [77],which is used as a medical illumination device.[82] The light-emitting device according to any one of [44] to [77],which is used as a work illumination device.[83] The light-emitting device according to any one of [44] to [77],which is used as an illumination device incorporated in industrialequipment.[84] The light-emitting device according to any one of [44] to [77],which is used as an illumination device for interior of transportation.[85] The light-emitting device according to any one of [44] to [77],which is used as an illumination device for works of art.[86] The light-emitting device according to any one of [44] to [77],which is used as an illumination device for aged persons.[87] A design method of a light-emitting device comprising at least asemiconductor light-emitting element as a light-emitting element,wherein light emitted from the light-emitting device is configured so asto include, in a main radiant direction thereof, light whose distanceD_(uvSSL) from a black-body radiation locus as defined by ANSI C78.377satisfies −0.0350≤D_(uvSSL)≤−0.0040, and

if a spectral power distribution of light emitted from thelight-emitting device in the radiant direction is denoted by ϕ_(SSL)(λ),a spectral power distribution of a reference light that is selectedaccording to T_(SSL) (K) of the light emitted from the light-emittingdevice in the radiant direction is denoted by ϕ_(ref)(λ), tristimulusvalues of the light emitted from the light-emitting device in theradiant direction are denoted by (X_(SSL), Y_(SSL), Z_(SSL)), andtristimulus values of the reference light that is selected according toT_(SSL) (K) of the light emitted from the light-emitting device in theradiant direction are denoted by (X_(ref), Y_(ref), Z_(ref)), and

if a normalized spectral power distribution S_(SSL)(λ) of light emittedfrom the light-emitting device in the radiant direction, a normalizedspectral power distribution S_(ref)(λ) of a reference light that isselected according to T_(SSL) (K) of the light emitted from thelight-emitting device in the radiant direction, and a difference ΔS (λ)between these normalized spectral power distributions are respectivelydefined as

S _(SSL)(λ)=ϕ_(SSL)(λ)/Y _(SSL),

S _(ref)(λ)=ϕ_(ref)(λ)/Y _(ref) and

ΔS(λ)=S _(ref)(λ)−S _(SSL)(λ) and

a wavelength that produces a longest wavelength local maximum value ofS_(SSL)(λ) in a wavelength range from 380 nm to 780 nm is denoted byλ_(R) (nm), then a wavelength Λ4 that assumes S_(SSL)(λ_(R))/2 exists ona longer wavelength-side of λ_(R), and

an index A_(cg) represented by formula (3) below satisfies−360≤A_(cg)≤−10

[Expression 11]

A _(cg)=∫₃₈₀ ⁴⁹⁵ ΔS(λ)dλ+∫ ₄₉₅ ⁵⁹⁰(−ΔS(λ))dλ+∫ ₅₉₀ ^(Λ4) ΔS(λ)dλ  (3)

[88] A design method of a light-emitting device comprising at least asemiconductor light-emitting element as a light-emitting element,wherein

light emitted from the light-emitting device is configured so as toinclude, in a main radiant direction thereof, light whose distanceD_(uvSSL) from a black-body radiation locus as defined by ANSI C78.377satisfies −0.0350≤D_(uvSSL)≤−0.0040, and

if a spectral power distribution of light emitted from thelight-emitting device in the radiant direction is denoted by λ_(SSL)(λ),a spectral power distribution of a reference light that is selectedaccording to T_(SSL) (K) of the light emitted from the light-emittingdevice in the radiant direction is denoted by ϕ_(ref)(λ), tristimulusvalues of the light emitted from the light-emitting device in theradiant direction are denoted by (X_(SSL), Y_(SSL), Z_(SSL)), andtristimulus values of the reference light that is selected according toT_(SSL) (K) of the light emitted from the light-emitting device in theradiant direction are denoted by (X_(ref), Y_(ref), Z_(ref)), and

if a normalized spectral power distribution S_(SSL)(λ) of light emittedfrom the light-emitting device in the radiant direction, a normalizedspectral power distribution S_(ref)(λ) of reference light that isselected according to T_(SSL) (K) of the light emitted from thelight-emitting device in the radiant direction, and a difference ΔS (λ)between these normalized spectral power distributions are respectivelydefined as

S _(SSL)(λ)=ϕ_(SSL)(λ)/Y _(SSL),

S _(ref)(λ)=ϕ_(ref)(λ)/Y _(ref) and

ΔS(λ)=S _(ref)(λ)−S _(SSL)(λ) and

a wavelength that produces a longest wavelength local maximum value ofS_(SSL)(λ) in a wavelength range from 380 nm to 780 nm is denoted byλ_(R) (nm), then a wavelength Λ4 that assumes S_(SSL)(λ_(R))/2 does notexist on a longer wavelength-side of λ_(R), and

an index A_(cg) represented by formula (4) below satisfies−360≤A_(cg)≤−10

[Expression 12]

A _(cg)=∫₃₈₀ ⁴⁹⁵ ΔS(λ)dλ+∫ ₄₉₅ ⁵⁹⁰(−ΔS(λ))dλ+∫ ₅₉₀ ^(Λ4) ΔS(λ)dλ  (4).

According to the present invention, compared to a case whereillumination is performed with reference light (sometimes referred to asexperimental reference light), a case where illumination is performed bya light-emitting device emitting light which produces a color appearanceclose to reference light and which has a high R_(a) and a high R_(i)(sometimes referred to as experimental pseudo-reference light), and thelike, an illumination method and a light-emitting device are achievedwhich are capable of realizing a truly favorable color appearance ofobjects statistically judged by a large number of subjects to be morefavorable even at an approximately similar CCT and/or an approximatelysimilar illuminance.

Advantageous effects achieved by the present invention can be morespecifically exemplified as follows.

First, when illuminating with the illumination method according to thepresent invention or illuminating by a light-emitting device accordingto the present invention such as a light source, a fixture, or a system,compared to cases where illumination is performed with experimentalreference light or experimental pseudo-reference light, white appearswhiter, more natural, and more comfortable even at an approximatelysimilar CCT and/or an approximately similar illuminance. Furthermore,differences in lightness among achromatic colors such as white, gray,and black become more visible. As a result, for example, black lettersor the like on an ordinary sheet of white paper become more legible.Moreover, while details will be given later, such an effect iscompletely unexpected in the context of conventional wisdom.

Second, with illuminance when illuminating with the illumination methodaccording to the present invention or illuminance that is realized by alight-emitting device according to the present invention, a trulynatural color appearance as though viewed under several tens ofthousands of lx such as under outdoor illuminance on a sunny day isachieved for a majority of colors such as purple, bluish purple, blue,greenish blue, green, yellowish green, yellow, reddish yellow, red, andreddish purple, and in some cases, all colors even in an ordinary indoorenvironment of around several thousand lx to several hundred lx. Inaddition, the skin colors of subjects (Japanese), various foods,clothing, wooden colors, and the like which have intermediate chromaalso acquire a natural color appearance which many of the subjects feelmore favorable.

Third, when illuminating with the illumination method according to thepresent invention or illuminating by a light-emitting device accordingto the present invention, colors among close hues can be identified moreeasily and work or the like can be performed as comfortably as thoughunder a high-illuminance environment as compared to cases whereillumination is performed with experimental reference light orexperimental pseudo-reference light even at an approximately similar CCTand/or an approximately similar illuminance. Furthermore, specifically,for example, a plurality of lipsticks with similar red colors can bemore readily distinguished from each other.

Fourth, when illuminating with the illumination method according to thepresent invention or illuminating by a light source, a fixture, or asystem according to the present invention, objects can be viewed moreclearly and readily as though viewed under a high-illuminanceenvironment as compared to cases where illumination is performed withexperimental reference light or experimental pseudo-reference light evenat an approximately similar CCT and/or an approximately similarilluminance.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagram showing a spectral power distribution when assumingthat light, emitted from a packaged LED which incorporates asemiconductor light-emitting element with a peak wavelength of 459 nmand which comprises a green phosphor and a red phosphor, illuminates the15 Munsell renotation color samples, and a CIELAB color space on whichare respectively plotted a* values and b* values of the 15 Munsellrenotation color samples when illuminated by the LED and whenilluminated by reference light;

FIG. 2 is a diagram showing a spectral power distribution when assumingthat light, emitted from a packaged LED which incorporates asemiconductor light-emitting element with a peak wavelength of 475 nmand which comprises a green phosphor and a red phosphor, illuminates the15 Munsell renotation color samples, and a CIELAB color space on whichare respectively plotted a* values and b* values of the 15 Munsellrenotation color samples when illuminated by the LED and whenilluminated by reference light;

FIG. 3 is a diagram showing a spectral power distribution when assumingthat light, emitted from a packaged LED which incorporates asemiconductor light-emitting element with a peak wavelength of 425 nmand which comprises a green phosphor and a red phosphor, illuminates the15 Munsell renotation color samples, and a CIELAB color space on whichare respectively plotted a* values and b* values of the 15 Munsellrenotation color samples when illuminated by the LED and whenilluminated by reference light;

FIG. 4 is a diagram showing a spectral power distribution when assumingthat light, emitted from a packaged LED which incorporates asemiconductor light-emitting element with a peak wavelength of 459 nmand which comprises a green phosphor and a red phosphor, illuminates the15 Munsell renotation color samples, and a CIELAB color space on whichare respectively plotted a* values and b* values of the 15 Munsellrenotation color samples when illuminated by the LED and whenilluminated by reference light (Duv=0.0000);

FIG. 5 is a diagram showing a spectral power distribution when assumingthat light, emitted from a packaged LED which incorporates asemiconductor light-emitting element with a peak wavelength of 459 nmand which comprises a green phosphor and a red phosphor, illuminates the15 Munsell renotation color samples, and a CIELAB color space on whichare respectively plotted a* values and b* values of the 15 Munsellrenotation color samples when illuminated by the LED and whenilluminated by reference light (Duv=0.0100);

FIG. 6 is a diagram showing a spectral power distribution when assumingthat light, emitted from a packaged LED which incorporates asemiconductor light-emitting element with a peak wavelength of 459 nmand which comprises a green phosphor and a red phosphor, illuminates the15 Munsell renotation color samples, and a CIELAB color space on whichare respectively plotted a* values and b* values of the 15 Munsellrenotation color samples when illuminated by the LED and whenilluminated by reference light (Duv=0.0150);

FIG. 7 is a diagram showing a spectral power distribution when assumingthat light, emitted from a packaged LED which incorporates asemiconductor light-emitting element with a peak wavelength of 459 nmand which comprises a green phosphor and a red phosphor, illuminates the15 Munsell renotation color samples, and a CIELAB color space on whichare respectively plotted a* values and b* values of the 15 Munsellrenotation color samples when illuminated by the LED and whenilluminated by reference light (Duv=−0.0100);

FIG. 8 is a diagram showing a spectral power distribution when assumingthat light, emitted from a packaged LED which incorporates asemiconductor light-emitting element with a peak wavelength of 459 nmand which comprises a green phosphor and a red phosphor, illuminates the15 Munsell renotation color samples, and a CIELAB color space on whichare respectively plotted a* values and b* values of the 15 Munsellrenotation color samples when illuminated by the LED and whenilluminated by reference light (Duv=−0.0200);

FIG. 9 is a diagram showing a spectral power distribution when assumingthat light, emitted from a packaged LED which incorporates asemiconductor light-emitting element with a peak wavelength of 459 nmand which comprises a green phosphor and a red phosphor, illuminates the15 Munsell renotation color samples, and a CIELAB color space on whichare respectively plotted a* values and b* values of the 15 Munsellrenotation color samples when illuminated by the LED and whenilluminated by reference light (Duv=−0.0300);

FIG. 10 is a diagram showing a spectral power distribution when assumingthat light, emitted from a packaged LED which incorporates asemiconductor light-emitting element with a peak wavelength of 459 nmand which comprises a green phosphor and a red phosphor, illuminates the15 Munsell renotation color samples, and a CIELAB color space on whichare respectively plotted a* values and b* values of the 15 Munsellrenotation color samples when illuminated by the LED and whenilluminated by reference light (Duv=−0.0400);

FIG. 11 is a diagram showing a spectral power distribution when assumingthat light, emitted from a packaged LED which incorporates asemiconductor light-emitting element with a peak wavelength of 459 nmand which comprises a green phosphor and a red phosphor, illuminates the15 Munsell renotation color samples, and a CIELAB color space on whichare respectively plotted a* values and b* values of the 15 Munsellrenotation color samples when illuminated by the LED and whenilluminated by reference light (Duv=−0.0500);

FIG. 12 is a diagram showing a spectral power distribution when assumingthat light emitted from a packaged LED which incorporates foursemiconductor light-emitting elements illuminates the 15 Munsellrenotation color samples, and a CIELAB color space on which arerespectively plotted a* values and b* values of the 15 Munsellrenotation color samples when illuminated by the LED and whenilluminated by reference light (Duv=0.0000);

FIG. 13 is a diagram showing a spectral power distribution when assumingthat light emitted from a packaged LED which incorporates foursemiconductor light-emitting elements illuminates the 15 Munsellrenotation color samples, and a CIELAB color space on which arerespectively plotted a* values and b* values of the 15 Munsellrenotation color samples when illuminated by the LED and whenilluminated by reference light (Duv=0.0100);

FIG. 14 is a diagram showing a spectral power distribution when assumingthat light emitted from a packaged LED which incorporates foursemiconductor light-emitting elements illuminates the 15 Munsellrenotation color samples, and a CIELAB color space on which arerespectively plotted a* values and b* values of the 15 Munsellrenotation color samples when illuminated by the LED and whenilluminated by reference light (Duv=0.0200);

FIG. 15 is a diagram showing a spectral power distribution when assumingthat light emitted from a packaged LED which incorporates foursemiconductor light-emitting elements illuminates the 15 Munsellrenotation color samples, and a CIELAB color space on which arerespectively plotted a* values and b* values of the 15 Munsellrenotation color samples when illuminated by the LED and whenilluminated by reference light (Duv=0.0300);

FIG. 16 is a diagram showing a spectral power distribution when assumingthat light emitted from a packaged LED which incorporates foursemiconductor light-emitting elements illuminates the 15 Munsellrenotation color samples, and a CIELAB color space on which arerespectively plotted a* values and b* values of the 15 Munsellrenotation color samples when illuminated by the LED and whenilluminated by reference light (Duv=0.0400);

FIG. 17 is a diagram showing a spectral power distribution when assumingthat light emitted from a packaged LED which incorporates foursemiconductor light-emitting elements illuminates the 15 Munsellrenotation color samples, and a CIELAB color space on which arerespectively plotted a* values and b* values of the 15 Munsellrenotation color samples when illuminated by the LED and whenilluminated by reference light (Duv=−0.0100);

FIG. 18 is a diagram showing a spectral power distribution when assumingthat light emitted from a packaged LED which incorporates foursemiconductor light-emitting elements illuminates the 15 Munsellrenotation color samples, and a CIELAB color space on which arerespectively plotted a* values and b* values of the 15 Munsellrenotation color samples when illuminated by the LED and whenilluminated by reference light (Duv=−0.0200);

FIG. 19 is a diagram showing a spectral power distribution when assumingthat light emitted from a packaged LED which incorporates foursemiconductor light-emitting elements illuminates the 15 Munsellrenotation color samples, and a CIELAB color space on which arerespectively plotted a* values and b* values of the 15 Munsellrenotation color samples when illuminated by the LED and whenilluminated by reference light (Duv=−0.0300);

FIG. 20 is a diagram showing a spectral power distribution when assumingthat light emitted from a packaged LED which incorporates foursemiconductor light-emitting elements illuminates the 15 Munsellrenotation color samples, and a CIELAB color space on which arerespectively plotted a* values and b* values of the 15 Munsellrenotation color samples when illuminated by the LED and whenilluminated by reference light (Duv=−0.0400);

FIG. 21 is a diagram showing a spectral power distribution when assumingthat light emitted from a packaged LED which incorporates foursemiconductor light-emitting elements illuminates the 15 Munsellrenotation color samples, and a CIELAB color space on which arerespectively plotted a* values and b* values of the 15 Munsellrenotation color samples when illuminated by the LED and whenilluminated by reference light (Duv=−0.0500);

FIG. 22 is a diagram showing a spectral power distribution when assumingthat light, emitted from a packaged LED which incorporates asemiconductor light-emitting element with a peak wavelength of 405 nmand which comprises a blue phosphor, a green phosphor, and a redphosphor, illuminates the 15 Munsell renotation color samples, and aCIELAB color space on which are respectively plotted a* values and b*values of the 15 Munsell renotation color samples when illuminated bythe LED and when illuminated by reference light (Duv=0.0001);

FIG. 23 is a diagram showing a spectral power distribution when assumingthat light, emitted from a packaged LED which incorporates asemiconductor light-emitting element with a peak wavelength of 405 nmand which comprises a blue phosphor, a green phosphor, and a redphosphor, illuminates the 15 Munsell renotation color samples, and aCIELAB color space on which are respectively plotted a* values and b*values of the 15 Munsell renotation color samples when illuminated bythe LED and when illuminated by reference light (Duv=0.0100);

FIG. 24 is a diagram showing a spectral power distribution when assumingthat light, emitted from a packaged LED which incorporates asemiconductor light-emitting element with a peak wavelength of 405 nmand which comprises a blue phosphor, a green phosphor, and a redphosphor, illuminates the 15 Munsell renotation color samples, and aCIELAB color space on which are respectively plotted a* values and b*values of the 15 Munsell renotation color samples when illuminated bythe LED and when illuminated by reference light (Duv=0.0194);

FIG. 25 is a diagram showing a spectral power distribution when assumingthat light, emitted from a packaged LED which incorporates asemiconductor light-emitting element with a peak wavelength of 405 nmand which comprises a blue phosphor, a green phosphor, and a redphosphor, illuminates the 15 Munsell renotation color samples, and aCIELAB color space on which are respectively plotted a* values and b*values of the 15 Munsell renotation color samples when illuminated bythe LED and when illuminated by reference light (Duv=0.0303);

FIG. 26 is a diagram showing a spectral power distribution when assumingthat light, emitted from a packaged LED which incorporates asemiconductor light-emitting element with a peak wavelength of 405 nmand which comprises a blue phosphor, a green phosphor, and a redphosphor, illuminates the 15 Munsell renotation color samples, and aCIELAB color space on which are respectively plotted a* values and b*values of the 15 Munsell renotation color samples when illuminated bythe LED and when illuminated by reference light (Duv=0.0401);

FIG. 27 is a diagram showing a spectral power distribution when assumingthat light, emitted from a packaged LED which incorporates asemiconductor light-emitting element with a peak wavelength of 405 nmand which comprises a blue phosphor, a green phosphor, and a redphosphor, illuminates the 15 Munsell renotation color samples, and aCIELAB color space on which are respectively plotted a* values and b*values of the 15 Munsell renotation color samples when illuminated bythe LED and when illuminated by reference light (Duv=0.0496);

FIG. 28 is a diagram showing a spectral power distribution when assumingthat light, emitted from a packaged LED which incorporates asemiconductor light-emitting element with a peak wavelength of 405 nmand which comprises a blue phosphor, a green phosphor, and a redphosphor, illuminates the 15 Munsell renotation color samples, and aCIELAB color space on which are respectively plotted a* values and b*values of the 15 Munsell renotation color samples when illuminated bythe LED and when illuminated by reference light (Duv=−0.0100);

FIG. 29 is a diagram showing a spectral power distribution when assumingthat light, emitted from a packaged LED which incorporates asemiconductor light-emitting element with a peak wavelength of 405 nmand which comprises a blue phosphor, a green phosphor, and a redphosphor, illuminates the 15 Munsell renotation color samples, and aCIELAB color space on which are respectively plotted a* values and b*values of the 15 Munsell renotation color samples when illuminated bythe LED and when illuminated by reference light (Duv=−0.0200);

FIG. 30 is a diagram showing a spectral power distribution when assumingthat light, emitted from a packaged LED which incorporates asemiconductor light-emitting element with a peak wavelength of 405 nmand which comprises a blue phosphor, a green phosphor, and a redphosphor, illuminates the 15 Munsell renotation color samples, and aCIELAB color space on which are respectively plotted a* values and b*values of the 15 Munsell renotation color samples when illuminated bythe LED and when illuminated by reference light (Duv=−0.0303);

FIG. 31 is a diagram showing a spectral power distribution when assumingthat light, emitted from a packaged LED which incorporates asemiconductor light-emitting element with a peak wavelength of 405 nmand which comprises a blue phosphor, a green phosphor, and a redphosphor, illuminates the 15 Munsell renotation color samples, and aCIELAB color space on which are respectively plotted a* values and b*values of the 15 Munsell renotation color samples when illuminated bythe LED and when illuminated by reference light (Duv=−0.0403);

FIG. 32 is a diagram showing a spectral power distribution when assumingthat light, emitted from a packaged LED which incorporates asemiconductor light-emitting element with a peak wavelength of 405 nmand which comprises a blue phosphor and a red phosphor, illuminates the15 Munsell renotation color samples, and a CIELAB color space on whichare respectively plotted a* values and b* values of the 15 Munsellrenotation color samples when illuminated by the LED and whenilluminated by reference light (Duv=−0.0448);

FIG. 33 is a diagram showing an integral range for a parameter A_(cg)(when a CCT is 5000 K or higher);

FIG. 34 is a diagram showing an integral range of the parameter A_(cg)(when a CCT is lower than 5000 K);

FIG. 35 is a diagram showing a normalized test light spectral powerdistribution (solid line) of test light 5 and a normalized referencelight spectral power distribution (dotted line) of calculationalreference light corresponding to the test light 5;

FIG. 36 is a diagram showing a CIELAB color space on which arerespectively plotted a* values and b* values of the 15 Munsellrenotation color samples when respectively assuming a case (solid line)where an object is illuminated by the test light 5 and a case where theobject is illuminated by calculational reference light corresponding tothe test light 5;

FIG. 37 is a diagram showing a normalized test light spectral powerdistribution (solid line) of test light 15 and a normalized referencelight spectral power distribution (dotted line) of calculationalreference light corresponding to the test light 15;

FIG. 38 is a diagram showing a CIELAB color space on which arerespectively plotted a* values and b* values of the 15 Munsellrenotation color samples when respectively assuming a case (solid line)where an object is illuminated by the test light 15 and a case where theobject is illuminated by calculational reference light corresponding tothe test light 15;

FIG. 39 is a diagram showing a normalized test light spectral powerdistribution (solid line) of test light 19 and a normalized referencelight spectral power distribution (dotted line) of calculationalreference light corresponding to the test light 19;

FIG. 40 is a diagram showing a CIELAB color space on which arerespectively plotted a* values and b* values of the 15 Munsellrenotation color samples when respectively assuming a case (solid line)where an object is illuminated by the test light 19 and a case where theobject is illuminated by calculational reference light corresponding tothe test light 19;

FIG. 41 is a diagram showing a normalized test light spectral powerdistribution (solid line) of comparative test light 14 and a normalizedreference light spectral power distribution (dotted line) ofcalculational reference light corresponding to the comparative testlight 14; and

FIG. 42 is a diagram showing a CIELAB color space on which arerespectively plotted a* values and b* values of the 15 Munsellrenotation color samples when respectively assuming a case (solid line)where an object is illuminated by the comparative test light 14 and acase where the object is illuminated by calculational reference lightcorresponding to the comparative test light 14.

BEST MODE FOR CARRYING OUT THE INVENTION

While the present invention will be described in detail hereinafter, itis to be understood that the present invention is not limited to theembodiments described below and that various modifications can be madewithout departing from the spirit and scope of the invention.

Moreover, an illumination method according to a first embodiment of thepresent invention specifies the invention based on light at a positionwhere an object is illuminated in a case where light emitted from alight-emitting device used in the illumination method illuminates theobject. Therefore, illumination methods used by light-emitting devicescapable of emitting light at a “position where an object is illuminated”which meets requirements of the present invention are to be included inthe spirit and scope of the present invention.

In addition, second and third embodiments of the present inventionspecify the invention based on light in a “main radiant direction” amonglight emitted from a light-emitting device. Therefore, light-emittingdevices capable of radiating light including light in a “main radiantdirection” which meets requirements of the present invention are to beincluded in the spirit and scope of the present invention.

As used herein, the “main radiant direction” according to the second andthird embodiments of the present invention refers to a direction inwhich light is radiated over a suitable range and in a suitableorientation which are in line with usage of the light-emitting device.

For example, the “main radiant direction” may be a direction in whichluminous intensity or luminance of the light-emitting device is maximumor locally maximum.

In addition, the “main radiant direction” may be a direction having afinite range including a direction in which the luminous intensity orthe luminance of the light-emitting device is maximum or locallymaximum.

Alternatively, the “main radiant direction” may be a direction in whichradiant intensity or radiance of the light-emitting device is maximum orlocally maximum.

In addition, the “main radiant direction” may be a direction having afinite range including a direction in which the radiant intensity or theradiance of the light-emitting device is maximum or locally maximum.

Specific examples will be given below.

When the light-emitting device is an individual light-emitting diode(LED), an individual packaged LED, an individual LED module, anindividual LED bulb, an individual composite lamp constituted by afluorescent lamp and a semiconductor light-emitting element, anindividual composite lamp constituted by an incandescent bulb and asemiconductor light-emitting element, or the like, a main radiantdirection may be a vertical direction of each light-emitting device orwithin a finite solid angle which includes the vertical direction andwhich ranges between, for example, a maximum of π(sr) and a minimum ofπ/100 (sr).

When the light-emitting device is an LED lighting fixture in which alens, a reflection mechanism, and the like is added to the packaged LEDor the like or a lighting fixture which incorporates a fluorescent lampand a semiconductor light-emitting element and which has lightdistribution characteristics applicable to so-called direct lightinguse, semi-direct lighting use, general diffused lighting use,direct/indirect lighting use, semi-indirect lighting use, and indirectlighting use, a main radiant direction may be a vertical direction ofeach light-emitting device or within a finite solid angle which includesthe vertical direction and which ranges between, for example, a maximumof π(sr) and a minimum of π/100 (sr). In addition, the main radiantdirection may be a direction in which luminous intensity or luminance ofthe light-emitting device is maximum or locally maximum. Furthermore,the main radiant direction may be within a finite solid angle thatincludes a direction in which luminous intensity or luminance of thelight-emitting device is maximum or locally maximum and which rangesbetween, for example, a maximum of π(sr) and a minimum of π/100 (sr). Inaddition, the main radiant direction may be a direction in which radiantintensity or radiance of the light-emitting device is maximum or locallymaximum. Furthermore, the main radiant direction may be within a finitesolid angle which includes a direction in which radiant intensity orradiance of the light-emitting device is maximum or locally maximum andwhich ranges between, for example, a maximum of π(sr) and a minimum ofπ/100 (sr).

When the light-emitting device is a lighting system in which a pluralityof the LED lighting fixtures or lighting fixtures incorporating afluorescent lamp is mounted, the main radiant direction may be avertical direction of a planar center of each light-emitting device orwithin a finite solid angle which includes the vertical direction andwhich ranges between, for example, a maximum of π(sr) and a minimum ofπ/100 (sr). In addition, the main radiant direction may be a directionin which luminous intensity or luminance of the light-emitting device ismaximum or locally maximum. Furthermore, the main radiant direction maybe within a finite solid angle which includes a direction in whichluminous intensity or luminance of the light-emitting device is maximumor locally maximum and which ranges between, for example, a maximum ofπ(sr) and a minimum of π/100 (sr). In addition, the main radiantdirection may be a direction in which radiant intensity or radiance ofthe light-emitting device is maximum or locally maximum. Furthermore,the main radiant direction may be within a finite solid angle whichincludes a direction in which radiant intensity or radiance of thelight-emitting device is maximum or locally maximum and which rangesbetween, for example, a maximum of π(sr) and a minimum of π/100 (sr).

A spectral power distribution of light emitted in the main radiantdirection by the light-emitting device is favorably measured at adistance where illuminance at a measuring point is a practicalilluminance (as will be described later, 150 lx or higher and 5000 lx orlower).

In the present specification, reference light as defined by CIE which isused in calculations for estimating a mathematical color appearance maysometimes be referred to as reference light, calculational referencelight, and the like. On the other hand, experimental reference lightwhich is used when making actual visual comparisons or, in other words,light from an incandescent bulb which incorporates a tungsten filamentor the like may sometimes be referred to as reference light,experimental reference light and the like. In addition, light with ahigh R_(a) and a high R_(i) which is estimated to have a colorappearance that is close to reference light such as light from an LEDlight source which is used as alternate light for experimental referencelight in a visual comparison experiment may sometimes be referred to asreference light, experimental pseudo-reference light and the like.Furthermore, light that is an object of a mathematical or experimentalexamination may sometimes be referred to as test light in contrast toreference light.

The light-emitting device used in the illumination method according tothe first embodiment of the present invention includes a semiconductorlight-emitting element that is a light-emitting element. In addition,the light-emitting device according to the second embodiment of thepresent invention includes a semiconductor light-emitting element thatis a light-emitting element. Configurations other than the above are notparticularly limited, and an individual semiconductor light-emittingelement to which a lead or the like as a conducting mechanism is addedor a packaged LED to which a heat dissipating mechanism is further addedand integrated with a phosphor or the like may be adopted. In addition,an LED module in which a robust heat dissipating mechanism is added toone or more packaged LEDs and which is generally mounted with aplurality of packaged LEDs may be adopted. Furthermore, an LED lightingfixture in which a lens, a light-reflecting mechanism, and the like areadded to a packaged LED and the like may be adopted. Moreover, alighting system which supports a large number of LED lighting fixturesor the like and which is configured to be capable of illuminating anobject may be adopted. The light-emitting device according to thepresent embodiment encompasses all of the above.

Hereinafter, the present invention will be described in detail.

The present inventor has discovered a radiometric property or aphotometric property common to spectra or spectral power distributionscapable of realizing a color appearance or an object appearance which isas natural, vivid, highly visible, and comfortable as though perceivedoutdoors in a high-illuminance environment even in an ordinary indoorilluminance environment. The present inventor further ascertained, froma colorimetric perspective, in what way the color appearance of thecolor samples having specific spectral reflectance characteristics whenassuming that the color is illuminated by light having theaforementioned spectrum or spectral power distribution changes (or doesnot change) when the object described above is achieved in comparisonwith a case where illumination by calculational reference light isassumed, and collectively reached the present invention. It should benoted that the present invention was made based on experimental factswhich defy common and conventional wisdom. Specific circumstancesleading to the invention can be summarized as follows.

[Summary of Circumstances Leading to Invention]

As a first step, a baseline mathematical examination was conducted onthe assumption of: A) a packaged LED light source incorporating both asemiconductor light-emitting element and a phosphor; and B) a packagedLED light source which does not include a phosphor and which onlyincorporates a semiconductor light-emitting element as a light-emittingelement, which both have a high degree of freedom in setting a spectralpower distribution.

In doing so, by employing, as a guideline, a mathematical variationregarding the color appearance of a color sample having specificspectral reflectance characteristics between a case where illuminationby calculational reference light is assumed and a case whereillumination by test light that is an examination object is assumed,test lights causing changes in hue, saturation (chroma), or the likewere examined in detail. In particular, while being aware of the Hunteffect in an ordinary indoor environment where illuminance drops toaround 1/10 to 1/1000 as compared to outdoors, the mathematicalexamination focused on light with variations in saturation of colorappearance of illuminated objects.

As a second step, prototypes of a packaged LED light source and alighting fixture incorporating the packaged LED light source were madebased on the mathematically examined test light. In addition, forcomparative visual experiments to be performed in a third step, anincandescent bulb with a tungsten filament was prepared as experimentalreference light. Furthermore, prototypes of a light source capable ofemitting light (experimental pseudo-reference light) with high R_(a) andhigh R_(i) and which produces a color appearance that is close to thatof calculational reference light as well as a lighting fixtureincorporating the light source were also made. Moreover, for visualexperiments using the above, in order to have subjects evaluate a colorappearance when an object is illuminated by experimental reference lightor experimental pseudo-reference light and a color appearance when theobject is illuminated by light (test light) of a lighting fixtureincorporating the packaged LED light source, an illumination experimentsystem capable of illuminating different illuminating light on a largenumber of observation objects was fabricated.

As a third step, comparative visual experiments were performed. Dueconsideration was given to preparing chromatic objects so that colors ofthe observation objects covered all hues including purple, bluishpurple, blue, greenish blue, green, yellowish green, yellow, reddishyellow, red, and reddish purple. Achromatic objects such as whiteobjects and black objects were also prepared. These chromatic andachromatic objects were prepared in wide varieties and in large numbersincluding still objects, fresh flowers, food, clothing, and printedmaterial. At this point, the subjects were asked to evaluate a colorappearance when the objects were illuminated by experimental referencelight or experimental pseudo-reference light and a color appearance whenthe objects were illuminated by test light. Comparisons between theformer and the latter were performed at similar CCTs and similarilluminance. The subjects were asked to perform evaluations from theperspective of which of the lights had relatively achieved a colorappearance or an object appearance that is as natural, vivid, highlyvisible, and comfortable as though perceived outdoors. The subjects werealso asked the reasons for their judgment regarding which is superior orinferior.

As a fourth step, radiometric properties and photometric properties ofthe experimental reference light/experimental pseudo-reference light andthe test light were extracted from actual measured values. Furthermore,a difference in colorimetric properties regarding a color appearance ofcolor samples having specific spectral reflectance characteristics whichdiffers from the observation objects described above between a casewhere illumination at a spectral power distribution of calculationalreference light is calculationally assumed and a case where illuminationat a spectral power distribution of an actually measured experimentalreference light/experimental pseudo-reference light/test light iscalculationally assumed was compared with the evaluations by thesubjects in the visual experiments, and characteristics of theillumination method or the light-emitting device determined to be trulycomfortable were extracted. Moreover, contents of the third and fourthsteps also represent examples/comparative examples of the illuminationmethod according to the first embodiment of the present invention, andcontents of the second, third, and fourth steps also representexamples/comparative examples of the second and third embodiments of thepresent invention.

[Quantification Method of Color Samples' Selection and Color Appearance]

In the first step, in consideration of the Hunt effect, a spectral powerdistribution at a position where light emitted from a light-emittingdevice mainly examined in the illumination method according to thepresent invention illuminates an object or a spectral power distributionof light in a main radiant direction which is emitted by thelight-emitting device according to the present invention was assumed tovary saturation of an illuminated object from a case where illuminationis performed using reference light. At this point, the followingselections were made in order to quantify a color appearance or avariation thereof.

It was considered that, in order to quantitatively evaluate a colorappearance from a spectral power distribution, a color sample withobvious mathematical spectral reflectance characteristics is favorablydefined and a difference in color appearance of the color sample betweena case of illumination by calculational reference light and a case ofillumination by test light is adopted as an index.

Although test colors used in CRI are general choices, color samples R₁to R₈ which are used when deriving an average color rendering index orthe like are color samples with intermediate chroma and were thereforeconsidered unsuitable when discussing saturation of high-chroma colors.In addition, while R₉ to R₁₂ are high-chroma color samples, there arenot enough samples for a detailed discussion covering a range of all hueangles.

Therefore, it was decided that 15 color samples (one color sample perhue) be selected from color samples which have the highest chroma andwhich are positioned outermost in a Munsell color circle according tothe Munsell renotation color system. Moreover, these are the same colorsamples used in CQS (Color Quality Scale) (versions 7.4 and 7.5) that isa new color rendition metric proposed by NIST (National Institute ofStandards and Technology), U.S.A. The 15 color samples used in thepresent invention will be listed below. In addition, a number assignedfor convenience sake are provided before each color sample. Moreover, inthe present specification, these numbers will sometimes be representedby n. For example, n=3 signifies “5PB 4/12”. n denotes a natural numberfrom 1 to 15.

#01 7.5P 4/10

#02 10PB 4/10

#03 5PB 4/12

#04 7.5B 5/10

#05 10BG 6/8

#06 2.5BG 6/10

#07 2.5G 6/12

#08 7.5GY 7/10

#09 2.5GY 8/10

#10 5Y 8.5/12

#11 10YR 7/12

#12 5YR 7/12

#13 10R 6/12

#14 5R 4/14

#15 7.5RP 4/12

In the present invention, from the perspective of deriving variousindices, an attempt was made to quantify in what way the colorappearance of the 15 color samples listed above changes (or does notchange) between a case where the colors are assumed to be illuminated bycalculational reference light and a case where the colors are assumed tobe illuminated by test light when a color appearance or an objectappearance that is as natural, vivid, highly visible, and comfortable asthough perceived in an outdoor high-illuminance environment is achievedeven in an ordinary indoor illuminance environment, and to extractresults of the quantification as a color rendering property that shouldbe attained by a light-emitting device.

Moreover, selection of a color space and selection of a chromaticadaptation formula are also important when quantitatively evaluatingcolor appearance that is mathematically derived from the spectral powerdistributions described above. In the present invention, CIE 1976 L*a*b*(CIELAB) that is a uniform color space currently recommended by the CIEwas used. In addition, CMCCAT2000 (Colour Measurement Committee'sChromatic Adaptation Transform of 2000) was adopted for chromaticadaptation calculation.

[Chromaticity Points Derived from Spectral Power Distribution atPosition where Object is Illuminated or from Spectral Power Distributionof Light in Main Radiant Direction Emitted from Light-Emitting Device]

In the first step, selection of a chromaticity point of a light sourceis also important when making various prototypes of a packaged LED lightsource. Although chromaticity derived from a light source, a spectralpower distribution at a position where an object is illuminated by lightfrom the light source, or a spectral power distribution of light in amain radiant direction emitted from a light-emitting device can bedefined by, for example, a CIE 1931 (x,y) chromaticity diagram, thederived chromaticity is favorably discussed using a CIE 1976 (u′,v′)chromaticity diagram which is a more uniform chromaticity diagram. Inaddition, when describing a position on a chromaticity diagram using aCCT and D_(uv), a (u′, (2/3)v′) chromaticity diagram (synonymous with aCIE 1960 (u,v) chromaticity diagram) is particularly used. Moreover,D_(uv) as described in the present specification is an amount defined byANSI C78.377 and represents a distance of closest approach to ablack-body radiation locus on a (u′, (2/3)v′) chromaticity diagram as anabsolute value thereof. Furthermore, a positive sign means that achromaticity point of a light-emitting device is above (on a side wherev′ is greater than) the black-body radiation locus, and a negative signmeans that the chromaticity point of the light-emitting device is below(on a side where v′ is smaller than) the black-body radiation locus.

[Examination of Calculation Regarding Saturation and D_(uv) Value]

The color appearance of an object can vary even if the chromaticitypoint remains the same. For example, the three spectral powerdistributions (test lights) shown in FIGS. 1, 2, and 3 represent anexample where the color appearance of an illuminated objects is variedat a same chromaticity (CCT=5500 K, D_(uv)=0.0000) when assuming apackaged LED which incorporates a semiconductor light-emitting elementwith a peak wavelength from 425 to 475 nm and which uses thesemiconductor light-emitting element as an excitation light source of agreen phosphor and a red phosphor. While it is assumed that samematerials are used for the green phosphor and the red phosphorconstituting the respective spectral power distributions, in order tovary saturation, peak wavelengths of blue semiconductor light-emittingelements were respectively set to 459 nm for FIG. 1, 475 nm for FIG. 2,and 425 nm for FIG. 3. Expected color appearances of the 15 colorsamples when assuming illumination at the respective spectral powerdistributions and illumination by calculational reference lightscorresponding to the respective spectral power distributions are asdepicted in the CIELAB color spaces in FIGS. 1 to 3. In the drawings,points connected by dotted lines represent illumination by calculationalreference light and points connected by solid lines representillumination by test light. Moreover, while a direction perpendicular tothe plane of paper represents lightness, only a* and b* axes wereplotted for the sake of convenience.

The following findings were made regarding the spectral powerdistribution shown in FIG. 1. Based on calculations assumingillumination by calculational reference light and calculations assumingillumination by the test lights shown in the drawings, it was predictedthat the color appearances of the 15 color samples will closely resembleone another. In addition, Ra calculated based on the spectral powerdistribution was high at 95. In a case where illumination by the testlight shown in FIG. 2 is assumed, it was predicted that red and bluewill appear vivid but purple and green will dull as compared to a casewhere illumination by calculational reference light is assumed. Racalculated based on the spectral power distribution was relatively lowat 76. Conversely, in a case where illumination by the test light shownin FIG. 3 is assumed, it was predicted that purple and green will appearvivid but red and blue will dull as compared to a case whereillumination by calculational reference light is assumed. Ra calculatedbased on the spectral power distribution was relatively low at 76.

As described above, it was found that color appearances can be varied atthe same chromaticity point.

However, a detailed examination by the present inventor revealed that adegree of freedom of light in a vicinity of a black-body radiation locusor, in other words, light whose D_(uv) is in a vicinity of 0 isinsufficient to vary spectral power distribution and vary the colorappearance of the 15 high-saturation color samples. A more specificdescription will be given below.

For example, as shown in FIGS. 2 and 3, opposite tendencies werepredicted for a variation in saturation of red/blue and a variation insaturation of purple/green. In other words, it was predicted that whensaturation of a certain hue increases, saturation of another huedecreases. In addition, according to another examination, it wasdifficult to simultaneously vary saturation of a large number of huesusing a simple and feasible method. Therefore, when illuminating withlight in a vicinity of a black-body radiation locus or light whoseD_(uv) is in a vicinity of 0, it was difficult to simultaneously varysaturation of a large number of hues of the 15 high-chroma colorsamples, to relatively uniformly increase or decrease saturation of manyhues, and the like.

In consideration thereof, the present inventor mathematically examinedcolor appearances of the 15 color samples when assigning differentD_(uv) values to a plurality of spectral power distributions whilecomparing with a case where illumination is performed by calculationalreference light. Generally, it is thought that white appears greenishwhen D_(uv) is biased toward positive, white appears reddish when D_(uv)takes a negative value, and overall color appearance becomes unnaturalwhen D_(uv) deviates from the vicinity of 0. In particular, it isthought that coloring of white induces such perceptions. However, thepresent inventor conducted the following examination with an aim toincrease saturation controllability.

The eight spectral power distributions shown in FIGS. 4 to 11 representcalculation results of varying D_(uv) from −0.0500 to +0.0150 at a sameCCT (2700 K) when assuming a packaged LED which incorporates a bluesemiconductor light-emitting element with a peak wavelength of 459 nmand which uses the blue semiconductor light-emitting element as anexcitation light source of a green phosphor and a red phosphor. Expectedcolor appearances of the 15 color samples when assuming illumination atthe respective spectral power distributions (test lights) andillumination by calculational reference lights corresponding to therespective test lights are as represented in the CIELAB color spaces inFIGS. 4 to 11. In the drawings, points connected by dotted linesrepresent results regarding the calculational reference lights andpoints connected by solid lines represent results regarding respectivetest lights. Moreover, while a direction perpendicular to the plane ofpaper represents lightness, only a* and b* axes were plotted for thesake of convenience.

With the test light with D_(uv)=0.0000 shown in FIG. 4, it was predictedthat the color appearances of the 15 color samples will closely resembleone another between a case where illumination by calculational referencelight is assumed and a case where illumination by the test light shownin FIG. 4 is assumed. Ra calculated based on the spectral powerdistribution was high at 95.

The test lights shown in FIGS. 5 and 6 represent examples where D_(uv)is shifted in a positive direction from +0.0100 to +0.0150. As shown,when D_(uv) is shifted in the positive direction, it was predicted thatthe saturation of the 15 color samples can be varied over a wider huerange as compared to the case of the test light with D_(uv)=0.0000. Inaddition, it was found that the saturation of the 15 color samples canbe varied relatively uniformly as compared to the case of the test lightwith D_(uv)=0.0000. Moreover, with the case of the calculationalreference lights and the case of the test lights shown in FIGS. 5 and 6,it was predicted that the color appearances of almost all of the 15color samples with the exception of the blue to greenish blue regionwill dull when D_(uv) is shifted in the positive direction. Furthermore,a trend was also predicted in that the greater the shift of D_(uv) inthe positive direction, the lower the saturation. Ra calculated based onthe spectral power distributions of FIGS. 5 and 6 were 94 and 89,respectively.

On the other hand, the test lights shown in FIGS. 7 to 11 representexamples where D_(uv) is shifted in a negative direction from −0.0100 to−0.0500. As shown, when D_(uv) is shifted in the negative direction, itwas found that the saturation of the 15 color samples can be varied overa wider hue range as compared to the case of the test light withD_(uv)=0.0000. It was also found that the saturation of the 15 colorsamples can be varied relatively uniformly as compared to the case ofthe test light with D_(uv)=0.0000. Moreover, it was predicted that thecolor appearances of almost all of the 15 color samples with theexception of the blue to greenish blue region and the purple region willappear vividly when D_(uv) is shifted in the negative direction betweena case where illumination by the calculational reference lights isassumed and a case where illumination by the test lights shown in FIGS.7 to 11 is assumed. Furthermore, a trend was also predicted in that thegreater the shift of D_(uv) in the negative direction, the higher thesaturation. Ra calculated based on the spectral power distributions ofFIGS. 7 to 11 was 92, 88, 83, 77, and 71, respectively. According tocurrently prevailing belief, it was predicted that the greater the shiftof D_(uv) in the negative direction, the further the deviation of colorappearance from a case of illumination with reference light and,therefore, the greater the deterioration of color appearance.

In consideration thereof, the present inventor mathematically examinedpredictions of color appearances of the 15 most vivid color sampleswhich are positioned outermost in the Munsell renotation color systemwhen assigning various D_(uv) values to test lights in whichspectrum-forming light-emitting elements (light-emitting materials)differ from each other while comparing with calculational referencelights.

The 10 spectral power distributions shown in FIGS. 12 to 21 representresults of varying D_(uv) from −0.0500 to +0.0400 at a same CCT (4000 K)when a packaged LED incorporating four semiconductor light-emittingelements is assumed. Peak wavelengths of the four semiconductorlight-emitting elements were respectively set to 459 nm, 528 m, 591 nm,and 662 nm. Expected color appearances of the 15 color samples whenassuming illumination by the 10 respective test lights and illuminationby the calculational reference lights corresponding to the respectivetest lights are as represented in the CIELAB color spaces in FIGS. 12 to21. In the drawings, points connected by dotted lines represent resultsobtained with the calculational reference lights and points connected bysolid lines represent results regarding the respective test lights.Moreover, while a direction perpendicular to the plane of paperrepresents lightness, only a* and b* axes were plotted for the sake ofconvenience.

With the test light with D_(uv)=0.0000 shown in FIG. 12, it waspredicted that the color appearances of the 15 color samples willclosely resemble one another between a case where illumination by thecalculational reference light is assumed and a case where illuminationby the test light shown in FIG. 12 is assumed. Ra calculated based onthe spectral power distribution was high at 98.

The test lights shown in FIGS. 13 to 16 represent examples where D_(uv)is shifted in a positive direction from +0.0100 to +0.0400. As shown,when D_(uv) is shifted in the positive direction, it was found that thesaturation of the 15 color samples can be varied over a wider hue rangeas compared to the case of the test light with D_(uv)=0.0000. It wasalso found that the saturation of the 15 color samples can be variedrelatively uniformly as compared to the case of the test light withD_(uv)=0.0000. Moreover, it was predicted that the color appearances ofalmost all of the 15 color samples with the exception of the blue togreenish blue region and the red region will appear dull when D_(uv) isshifted in the positive direction between a case where illumination bythe calculational reference lights is assumed and a case whereillumination by the test lights shown in FIGS. 13 to 16 is assumed.Furthermore, a trend was also predicted in that the greater the shift ofD_(uv) in the positive direction, the lower the saturation. Racalculated based on the spectral power distributions of FIGS. 13 to 16was 95, 91, 86, and 77, respectively. According to currently prevailingbelief, it was predicted that the greater the shift of D_(uv) in thepositive direction, the further the deviation of color appearance from acase of illumination with reference light and, therefore, the greaterthe deterioration of color appearance.

On the other hand, the test lights shown in FIGS. 17 to 21 representexamples where D_(uv) is shifted in a negative direction from −0.0100 to−0.0500. As shown, when D_(uv) is shifted in the negative direction, itwas found that the saturation of the 15 color samples can be varied overa wider hue range as compared to the case of the test light withD_(uv)=0.0000. It was also found that the saturation of the 15 colorsamples can be varied relatively uniformly as compared to the case ofthe test light with D_(uv)=0.0000. Moreover, it was predicted that thecolor appearances of almost all of the 15 color samples with theexception of the blue to greenish blue region and the red region willappear vividly when D_(uv) is shifted in the negative direction betweena case where illumination by the calculational reference lights isassumed and a case where illumination by the test lights shown in FIGS.17 to 21 is assumed. Furthermore, a trend was also predicted in that thegreater the shift of D_(uv) in the negative direction, the higher thesaturation. Ra calculated based on the spectral power distributions ofFIGS. 17 to 21 was 95, 91, 86, 81, and 75, respectively. According tocurrently prevailing belief, it was predicted that the greater the shiftof D_(uv) in the negative direction, the further the deviation of colorappearance from a case of illumination with reference light and,therefore, the greater the deterioration of color appearance.

In addition, the present inventor mathematically examined predictions ofcolor appearances of the 15 most vivid color samples which arepositioned outermost in the Munsell renotation color system whenassigning various D_(uv) values to test lights in which spectrum-forminglight-emitting elements (light-emitting materials) further differ fromeach other while comparing with calculational reference light.

The 11 spectral power distributions shown in FIGS. 22 to 32 representcalculation results of varying D_(uv) from −0.0448 to +0.0496 at a closeCCT (approximately 5500 K) when assuming a packaged LED whichincorporates a purple semiconductor light-emitting element and whichuses the purple semiconductor light-emitting element as an excitationlight source of a blue phosphor, a green phosphor, and a red phosphor. Apeak wavelength of the incorporated semiconductor light-emitting elementwas set to 405 nm. Moreover, the result shown in FIG. 32 was obtainedwithout including a green phosphor in order to cause D_(uv) to take anexcessively negative value. Mathematically expected color appearances ofthe 15 color samples when assuming illumination by the 11 respectivetest lights and illumination by calculational reference lightscorresponding to the respective test lights are as represented in theCIELAB color spaces in FIGS. 22 to 32. In the drawings, points connectedby dotted lines represent results regarding the calculational referencelights and points connected by solid lines represent results regardingthe respective test lights. Moreover, while a direction perpendicular tothe plane of paper represents lightness, only a* and b* axes wereplotted for the sake of convenience.

With the test light with D_(uv)=0.0001 shown in FIG. 22, it waspredicted that the color appearances of the 15 color samples willclosely resemble one another between a case of the calculationalreference light and a case of the test light shown in FIG. 22. Racalculated based on the spectral power distribution was high at 96.

The test lights shown in FIGS. 23 to 27 represent examples where D_(uv)is shifted in a positive direction from +0.0100 to +0.0496. As shown,when D_(uv) is shifted in the positive direction, it was found that thesaturation of the 15 color samples can be varied over a wider hue rangeas compared to the case of the test light with D_(uv)=0.0001. It wasalso found that the saturation of the 15 color samples can be variedrelatively uniformly as compared to the case of the test light withD_(uv)=0.0001. Moreover, it was predicted that the color appearances ofalmost all of the 15 color samples with the exception of the blue regionwill appear dull when D_(uv) is shifted in the positive directionbetween a case where illumination by the calculational reference lightsis assumed and a case where illumination by the test lights shown inFIGS. 23 to 27 is assumed. Furthermore, a trend was also predicted inthat the greater the shift of D_(uv) in the positive direction, thelower the saturation. Ra calculated based on the spectral powerdistributions of FIGS. 23 to 27 was 92, 85, 76, 69, and 62,respectively. According to currently prevailing belief, it was predictedthat the greater the shift of D_(uv) in the positive direction, thefurther the deviation of color appearance from a case of illuminationwith reference light and, therefore, the greater the deterioration ofcolor appearance.

On the other hand, the test lights shown in FIGS. 28 to 32 representexamples where D_(uv) is shifted in a negative direction from −0.0100 to−0.0448. As described earlier, D_(uv)=−0.0448 is realized as a systemthat does not include a green phosphor. As shown, when D_(uv) is shiftedin the negative direction, it was found that the saturation of the 15color samples can be varied over a wider hue range as compared to thecase of the test light with D_(uv)=0.0001. It was also found that thesaturation of the 15 color samples can be varied relatively uniformly ascompared to the case of the test light with D_(uv)=0.0001. Moreover, itwas predicted that the color appearances of almost all of the 15 colorsamples with the exception of the blue region will appear vivid whenD_(uv) is shifted in the negative direction between a case whereillumination by the calculational reference lights is assumed and a casewhere illumination by the test lights shown in FIGS. 28 to 32 isassumed. Furthermore, a trend was also predicted in that the greater theshift of D_(uv) in the negative direction, the higher the saturation. Racalculated based on the spectral power distributions of FIGS. 28 to 32was 89, 80, 71, 61, and 56, respectively. According to currentlyprevailing belief, it was predicted that the greater the shift of D_(uv)in the negative direction, the further the deviation of color appearancefrom a case of illumination with reference light and, therefore, thegreater the deterioration of color appearance.

[Summary of Examination of Calculation Regarding Saturation Control andD_(uv) Value]

From the examination of calculations thus far, the following waspredicted “based on currently prevailing wisdom”.

(1) Test light with a chromaticity point in a vicinity of D_(uv)=0.0000has a low degree of freedom with respect to varying saturation of the 15color samples. Specifically, it is difficult to simultaneously varysaturation of a large number of hues of the 15 high-chroma colorsamples, to relatively uniformly increase or decrease saturation of manyhues, and the like.

(2) When D_(uv) of test light is set to a positive value, saturation ofthe 15 color samples can be lowered relatively easily. The saturation ofthe 15 color samples can be lowered over a wider hue range and in arelatively uniform manner as compared to the case of the test light withD_(uv)=0.0000. Furthermore, the greater the shift of D_(uv) in thepositive direction, the lower the saturation. In addition, since Rafurther decreases, it was predicted that in visual experiments or thelike, the greater the shift of D_(uv) in the positive direction, thegreater the deviation of color appearance in a case of illumination bytest light from a case where an actual illuminated objects or the likeis illuminated by experimental reference light or experimentalpseudo-reference light and, therefore, the greater the deterioration ofcolor appearance. In particular, it was predicted that white will appearyellowish (greenish) and overall color appearance will become unnatural.

(3) When D_(uv) is set to a negative value, saturation of the 15 colorsamples can be raised relatively easily. The saturation of the 15 colorsamples can be raised over a wider hue range and in a relatively uniformmanner as compared to the case of the test light with D_(uv)=0.0000.Furthermore, the greater the shift of D_(uv) in the negative direction,the higher the saturation. In addition, since Ra further decreases, itwas predicted that the greater the shift of D_(uv) in the negativedirection, the greater the deviation of color appearance in a case ofillumination by test light from a case where an actual illuminatedobjects or the like is illuminated by experimental reference light orexperimental pseudo-reference light and, therefore, the greater thedeterioration of color appearance. In particular, it was predicted thatwhite will appear reddish (pinkish) and overall color appearance willbecome unnatural.

The above are predictions made “based on currently prevailing wisdom”from the examination of calculations thus far.

[Introduction of Quantitative Indices]

In the present invention, the following quantitative indices wereintroduced in preparation of a detailed discussion regardingcharacteristics of a spectral power distribution or a color appearanceitself, luminous efficacy of radiation, and the like and in preparationof a detailed discussion regarding color appearance.

[Introduction of Quantitative Index Regarding Color Appearance]

First, it was decided that an a* value and a b* value of the 15 colorsamples in a CIE 1976 L*a*b* color space of test light as measured at aposition of an object when the object is illuminated by the test light(according to the illumination method of the present invention) and testlight when a light-emitting device emits the test light in a mainradiant direction (according to the light-emitting device of the presentinvention) be respectively denoted by a*_(nSSL) and b*_(nSSL) (where nis a natural number from 1 to 15), hue angles of the 15 color samples berespectively denoted by θ_(nSSL) (degrees) (where n is a natural numberfrom 1 to 15), an a* value and a b* value of the 15 color samples in aCIE 1976 L*a*b* color space when mathematically assuming illumination bycalculational reference light that is selected according to a CCT of thetest light (black-body radiator when lower than 5000 K and CIE daylightwhen equal to or higher than 5000 K) be respectively denoted bya*_(nref) and b*_(nref) (where n is a natural number from 1 to 15), hueangles of the 15 color samples be respectively denoted by θ_(nref)(degrees) (where n is a natural number from 1 to 15), and an absolutevalue of respective differences in hue angles Δh_(n)(degrees) (where nis a natural number from 1 to 15) of the 15 Munsell renotation colorsamples when illuminated by the two lights be defined as

|Δh _(n)|=|θ_(nSSL)−θ_(nref)|.

That is, |Δh_(n)| involves “Δh₁, Δh₂, Δh₃, . . . and Δh₁₅”.

This was done because mathematically-predicted differences in hue anglesrelated to the 15 Munsell renotation color samples specially selected inthe present invention were considered important indices for evaluatingvarious objects or color appearances of the objects as a whole andrealizing a color appearance or an object appearance that is natural,vivid, highly visible, and comfortable when performing visualexperiments using test light and experimental reference light orexperimental pseudo-reference light.

In addition, saturation differences ΔC_(n) (where n is a natural numberfrom 1 to 15) of the 15 Munsell renotation color samples when assumingillumination by two lights, namely, test light and calculationalreference light, were respectively defined as

ΔC _(n)=√{(a* _(nSSL))²+(b* _(nSSL))²}−√{(a* _(nref))²+(b* _(nref))²}.

Furthermore, formula (1) below which represents an average saturationdifference of the 15 Munsell renotation color samples was alsoconsidered to be an important index.

$\begin{matrix}\left\lbrack {{Expression}\mspace{14mu} 13} \right\rbrack & \; \\\frac{\sum\limits_{n = 1}^{15}{\Delta \; C_{n}}}{15} & (1)\end{matrix}$

Moreover, if a maximum saturation difference value among the 15 Munsellrenotation color samples is denoted by ΔC_(max) and a minimum saturationdifference value among the 15 Munsell renotation color samples isdenoted by ΔC_(min), then

(|ΔC _(max) −ΔC _(min)|)

representing a difference between the maximum saturation differencevalue and the minimum saturation difference value (difference amongdifferences between maximum and minimum degrees of saturation) was alsoconsidered an important index. This was done because variouscharacteristics related to differences in saturation among the 15Munsell renotation color samples specially selected in the presentinvention were considered important indices for evaluating variousobjects or color appearances of the objects as a whole and realizing acolor appearance or an object appearance that is natural, vivid, highlyvisible, and comfortable when performing visual experiments using testlight and experimental reference light or experimental pseudo-referencelight.

[Introduction of Quantitative Index Regarding Spectral PowerDistribution]

In the present invention, the following two quantitative indices wereintroduced in order to further discuss radiometric properties andphotometric properties of spectral power distributions. One is an indexA_(cg) and the other is luminous efficacy of radiation K (lm/W).

The index A_(cg) is an attempt to describe a difference between a colorappearance by experimental reference light or experimentalpseudo-reference light and a color appearance by test light as aradiometric property and a photometric property of a spectral powerdistribution or a spectrum shape. As a result of various examinations,the index A_(cg), has been defined in the present invention as follows.

Let ϕ_(ref)(λ) and ϕ_(SSL)(λ) respectively denote spectral powerdistributions of calculational reference light and test light whichrepresent color stimuli that differ from one another when measured at aposition of an illuminated objects (according to the illumination methodof the present invention) or when measuring light emitted in a mainradiant direction from a light-emitting device (according to thelight-emitting device of the present invention), x (λ), y (λ), and z (λ)denote a color-matching function, and (X_(ref), Y_(ref), Z_(ref)) and(X_(SSL), Y_(SSL), Z_(SSL)) respectively denote tristimulus valuescorresponding to the calculational reference light and the test light.In this case, the following is satisfied regarding the calculationalreference light and the test light, where k denotes a constant.

Y _(ref) =k∫ϕ _(ref)(λ)·y(λ)dλ

Y _(SSL) =k∫ϕ _(SSL)(λ)·y(λ)dλ

At this point, normalized spectral power distributions obtained bynormalizing the spectral power distributions of the calculationalreference light and the test light by their respective Y were defined as

S _(ref)(λ)=ϕ_(ref)(λ)/Y _(ref) and

S _(SSL)(λ)=ϕ_(SSL)(λ)/Y _(SSL),

and a difference between the normalized reference light spectral powerdistribution and the normalized test light spectral power distributionwas represented by

ΔS(λ)=S _(ref)(λ)−S _(SSL)(λ).

Furthermore, at this point, the index A_(cg) was defined as follows.

A _(cg)=∫₃₈₀ ⁴⁹⁵ ΔS(λ)dλ+∫ ₄₉₅ ⁵⁹⁰(−ΔS(λ))dλ+∫ ₅₉₀ ^(Λ4)ΔS(λ)dλ  [Expression 14]

Moreover, upper and lower limit wavelengths of the integrals wererespectively set toΛ1=380 nm,Λ2=495 nm, andΛ3=590 nm.

In addition, Λ4 was defined divided into the following two cases. First,in the normalized test light spectral power distribution S_(SSL)(λ),when a wavelength which provides a longest wavelength local maximumvalue within 380 nm to 780 nm is denoted by X_(R) (nm) and a spectralintensity of the wavelength λ_(R) (nm) is denoted by S_(SSL) (X_(R)), awavelength which is on a longer wavelength-side of h_(R) and which hasan intensity of S_(SSL) (%_(R))/2 was adopted as Λ4. If no suchwavelength exists within a range up to 780 nm, then Λ4 was set to 780nm.

The index A_(cg) is used when a visible range related to radiations thatare color stimuli is roughly divided into a short wavelength range (orthe blue region including purple and the like), an intermediatewavelength range (the green region including yellow and the like), and along wavelength range (the red region including orange and the like) inorder to determine whether a concave and/or a convex shape of a spectrumexist at an appropriate intensity and at an appropriate position in anormalized test light spectral power distribution as compared to amathematically normalized reference light spectral power distribution.As illustrated in FIGS. 33 and 34, long wavelength integral rangesdiffer according to positions of a longest wavelength local maximumvalue. In addition, selections of calculational reference light differaccording to a CCT of test light. In the case of FIG. 33, since the CCTof the test light depicted by a solid line in FIG. 33 is equal to orhigher than 5000 K, CIE daylight is selected as the reference light asdepicted by a dotted line in FIG. 33. In the case of FIG. 34, since theCCT of the test light depicted by a solid line in FIG. 34 is lower than5000 K, black-body radiator is selected as the reference light asdepicted by a dotted line in FIG. 34. Moreover, shaded portions in thedrawings schematically represent integral ranges of the short wavelengthrange, the intermediate wavelength range, and the long wavelength range.

In the short wavelength range, a first term of A_(cg) (an integral of ΔS(λ)) is more likely to have a negative value when a spectrum intensityof the normalized test light spectral power distribution is higher thanthat of the mathematically normalized reference light spectral powerdistribution. In the intermediate wavelength range, conversely, a secondterm of A_(cg) (an integral of −ΔS (λ)) is more likely to have anegative value when a spectrum intensity of the normalized test lightspectral power distribution is lower than that of the normalizedreference light spectral power distribution. Furthermore, in the longwavelength range, a third term of A_(cg) (an integral of ΔS (λ)) is morelikely to have a negative value when a spectrum intensity of thenormalized test light spectral power distribution is higher than that ofthe normalized reference light spectral power distribution.

In addition, as described earlier, the calculational reference lightvaries according to the CCT of the test light. In other words,black-body radiator is used as the calculational reference light whenthe CCT of the test light is lower than 5000 K, and defined CIE daylightis used as the calculational reference light when the CCT of the testlight is equal to or higher than 5000 K. When deriving a value of theindex A_(cg), mathematically defined black-body radiator or CIE daylightwas used for ϕ_(ref)(λ), while a function used in a simulation or avalue actually measured in an experiment was used for ϕ_(SSL)(λ).

Furthermore, when evaluating the test light spectral power distributionϕ_(SSL)(λ) when measured at a position of an illuminated objects(according to the illumination method of the present invention) or whenmeasuring light emitted in amain radiant direction from a light-emittingdevice (according to the light-emitting device of the presentinvention), the widely-used definition below was adopted for luminousefficacy of radiation K (lm/W).

K=Km×[∫ ₃₈₀ ⁷⁸⁰{ϕ_(SSL)(λ)×V(λ)}dλ]/[∫ ₃₈₀ ⁷⁸⁰ϕ_(SSL)(λ)dλ]  [Expression15]

In the equation above,

K_(m): maximum luminous efficacy (lm/W),

V (λ): spectral luminous efficiency, and

λ: wavelength (nm).

The luminous efficacy of radiation K (lm/W) of the test light spectralpower distribution ϕ_(SSL) (?) when measured at a position of anilluminated object (according to the illumination method of the presentinvention) or when measuring light emitted in a main radiant directionfrom a light-emitting device (according to the light-emitting device ofthe present invention) is an amount that equals luminous efficacy of asource η (lm/W) when an efficiency of the spectral power distributionwhich is attributable to its shape and which is related tocharacteristics of all materials constituting the light-emitting device(for example, efficiencies such as internal quantum efficiency and lightextraction efficiency of a semiconductor light-emitting element,internal quantum efficiency and external quantum efficiency of aphosphor, and light transmission characteristics of an encapsulant) is100%.

[Details of Second Step]

As described earlier, as the second step, prototypes of a packaged LEDlight source and a lighting fixture were made based on themathematically examined spectra (test lights). In addition, prototypesof a light source for light (experimental pseudo-reference light) with ahigh R_(a) and a high R_(i) and which produces a color appearance thatis close to that of calculational reference light as well as prototypesof a lighting fixture incorporating the light source were also made.

Specifically, prototypes of a light source that excites a green phosphorand a red phosphor using a blue semiconductor light-emitting element, alight source that excites a yellow phosphor and a red phosphor using ablue semiconductor light-emitting element, and a light source thatexcites a blue phosphor, a green phosphor, and a red phosphor using apurple semiconductor light-emitting element were made andinstrumentalized.

BAM or SBCA was used as the blue phosphor. BSS, β-SiAlON, or BSON wasused as the green phosphor. YAG was used as the yellow phosphor. CASONor SCASN was used as the red phosphor.

A normally practiced method was used when making packaged LEDprototypes. Specifically, a semiconductor light-emitting element (chip)was flip-chip-mounted on a ceramic package which incorporated metalwiring capable of providing electric contact. Next, a slurry created bymixing a phosphor to be used and a binder resin was arranged as aphosphor layer.

After the packaged LEDs were prepared, the packaged LEDs were used tocreate LED bulbs of MR16 Gu10 and MR16 Gu5.3, and the like. The LEDbulbs were made into a type of a lighting fixture by building a drivecircuit into the LED bulbs and also mounting a reflecting mirror, alens, and the like to the LED bulbs. In addition, some commerciallyavailable LED bulbs were also prepared. Furthermore, incandescent bulbsincorporating a tungsten filament were also prepared to be used asexperimental reference light.

In addition, a large number of the LED bulbs were arranged to produce alighting system for conducting comparative visual experiments. In thiscase, a system capable of illumination by instantaneously switchingamong three kinds of bulbs was assembled. A type of drive power wire wasdedicated for an incandescent bulb having a tungsten filament(experimental reference light), and an adjustable transformer wasarranged at a subsequent stage so that the CCT can be varied by boostingdrive voltage from 110 V to 130 V relative to 100 V input voltage.Furthermore, two remaining lines of the drive power wire were used forthe LED bulbs, in which one system was used for experimentalpseudo-reference light (LED light source) and the other for test light.

[Details of Third Step]

As the third step, comparative visual experiment were conducted in whichsubjects were asked to evaluate color appearances of a large number ofobservation objects while switching between experimental reference light(or experimental pseudo-reference light) and test light. The lightingsystem was installed in a dark room in order to remove disturbance. Inaddition, illuminance at the positions of the observation objects wasset approximately the same by varying the number of fixtures ofexperimental reference light (or experimental pseudo-reference light)and test light which were mounted to the lighting system. The experimentwas conducted within an illuminance range of approximately 150 lx toapproximately 5000 lx.

Illuminated objects and observed objects which were actually used willbe listed below. Due consideration was given to preparing chromaticobjects so that colors of all hues including purple, bluish purple,blue, greenish blue, green, yellowish green, yellow, reddish yellow,red, and reddish purple were represented. Achromatic objects such aswhite objects and black objects were also prepared. Illuminated objectswith color were prepared. In addition, these objects were prepared inwide varieties and in large numbers including still objects, freshflowers, food, clothing, and printed material. Furthermore, the skins ofthe subjects (Japanese) themselves were also included in the experimentas observation objects. Moreover, the color names partially added to theobject names listed below simply signify that such objects will appearin such colors in an ordinary environment and are not accuraterepresentations of the colors.

White ceramic plate, white asparagus, white mushroom, white gerbera,white handkerchief, white dress shirt, white rice, sesame and salt,salted rice crackerPurple fresh flowerBluish purple cloth handkerchief, blue jeans, greenish blue towel Greenbell pepper, lettuce, shredded cabbage, broccoli, green lime, greenappleYellow banana, yellow bell pepper, greenish yellow lemon, yellowgerbera, fried eggOrange orange, orange bell pepper, carrotRed tomato, red apple, red bell pepper, red sausage, pickled plum Pinknecktie, pink gerbera, salmon broiled with saltRusset necktie, beige work clothes, croquette, tonkatsu (deep-fried porkcutlet), burdock root, cookie, chocolatePeanut, woodenwareSkin of subjects (Japanese)Newspaper, color printed matter including black letters on whitebackground (polychromatic), paperback, weekly magazine Exterior wallcolor samples (Alpolic manufactured by Mitsubishi Plastics, Inc.; white,blue, green, yellow, red)Color checkers (Color checker classic manufactured by X-Rite; total of24 color samples including 18 chromatic colors and six achromatic colors(one white, four grey, and one black)).

Moreover, names and Munsell notations of the respective color samples inthe color checker are as follows.

Name Munsell Notation Dark skin 3.05 YR 3.69/3.20 Light skin 2.2 YR6.47/4.10 Blue sky 4.3 PB 4.95/5.55 Foliage 6.65 GY 4.19/4.15 Blueflower 9.65 PB 5.47/6.70 Bluish green 2.5 BG 7/6 Orange 5 YR 6/11Purplish blue 7.5 PB 4/10.7 Moderate red 2.5 R 5/10 Purple 5 P 3/7Yellow green 5 GY 7.08/9.1 Orange yellow 10 YR 7/10.5 Blue 7.5 PB2.90/12.75 Green 0.1 G 5.38/9.65 Red 5 R 4/12 Yellow 5 Y 8/11.1 Magenta2.5 RP 5/12 Cyan 5 B 5/8 White N 9.5/ Neutral 8 N 8/ Neutral 6.5 N 6.5/Neutral 5 N 5/ Neutral 3.5 N 3.5/ Black N 2/

Moreover, it is not always self-evident that a correlation existsbetween color appearances of the various illuminated objects used in thecomparative visual experiments and the various mathematical indicesrelated to the color appearances of the 15 Munsell color samples used inthe calculations. Such a correlation is to be revealed through thevisual experiments.

The visual experiments were performed by the following procedure.

The prepared experimental reference light, experimental pseudo-referencelight, and test light were divided per CCT as measured at the positionof illuminated objects (according to the illumination method of thepresent invention) or lights emitted in the main radiant directionsamong the prepared experimental reference light, experimentalpseudo-reference light, and test light were divided per CCT (accordingto the light-emitting device of the present invention) into sixexperiments. Details are as follows.

TABLE 1 CCT classification in visual experiments Experiment CCT range(K) A 2500 or higher lower than 2600 B 2600 or higher lower than 2700 C2700 or higher lower than 2900 D 2900 or higher lower than 3250 E 3500or higher lower than 4100 F 5400 or higher lower than 5700

In each visual experiment, a same object was illuminated by switchingbetween experimental reference light (or experimental pseudo-referencelight) and test light, and subjects were asked to relatively judge whichlight was capable of realizing a color appearance or an objectappearance that is as natural, vivid, highly visible, and comfortable asthough perceived outdoors. The subjects were also asked the reasons fortheir judgment regarding which is superior or inferior.

[Details of Fourth Step, Experiment Result]

In the fourth step, results of comparative visual experiments conductedin the third step using the prototypes of LED lightsources/fixtures/systems made in the second step were compiled. Table 2represents results corresponding to experiment A and Table 3 representsresults corresponding to experiment B. The same shall apply thereafter,with Table 7 representing results corresponding to experiment F.Regarding comprehensive evaluations of the test lights relative to thereference light shown in Tables 2 to 7, a comparable appearance isrepresented by a central “0”, an evaluation that the test light isslightly favorable is represented by “1”, an evaluation that the testlight is favorable is represented by “2”, an evaluation that the testlight is more favorable is represented by “3”, an evaluation that thetest light is extremely favorable is represented by “4”, and anevaluation that the test light is dramatically favorable is representedby “5”. On the other hand, an evaluation that the test light is slightlyunfavorable is represented by “−1”, an evaluation that the test light isunfavorable is represented by “−2”, an evaluation that the test light ismore unfavorable is represented by “−3”, an evaluation that the testlight is extremely unfavorable is represented by “−4”, and an evaluationthat the test light is dramatically unfavorable is represented by “−5”.

In the fourth step, in particular, an attempt was made to extract aradiometric property and a photometric property of a spectral powerdistribution shared by the test light from an actually measured spectrumin a case where the color appearance of an illuminated object whenilluminated by the test light was judged to be more favorable than whenilluminated by experimental reference light or experimentalpseudo-reference light in a visual experiment. In other words, withrespect to numerical values of A_(cg), luminous efficacy of radiation K(lm/W), CCT (K), D_(uv), and the like, characteristics of a position ofthe illuminated object (according to the illumination method of thepresent invention) and light emitted in the main radiant direction fromthe light-emitting device (according to the light-emitting device of thepresent invention) were extracted. At the same time, differences betweencolor appearances of the 15 color samples when assuming illumination bycalculational reference lights and color appearances of the 15 colorsamples when assuming a test light spectral power distribution actuallymeasured at the position of the illuminated object (according to theillumination method of the present invention) or a test light spectralpower distribution when actually measuring light emitted in the mainradiant direction from the light-emitting device (according to thelight-emitting device of the present invention) were also compiled using|Δh_(n)|,

$\begin{matrix}\left\lbrack {{Expression}\mspace{14mu} 16} \right\rbrack & \; \\{\frac{\sum\limits_{n - 1}^{15}{\Delta \; C_{n}}}{15},} & \;\end{matrix}$

ΔC_(n), and (|ΔC_(max)−ΔC_(min)|) as indices. Moreover, while values of|Δh_(n)| and ΔC_(n) vary when n is selected, in this case, maximum andminimum values are shown. These values are also described in Tables 2 to7. Moreover, since it was found that, with respect to the colorappearance of the illuminated object, results of comprehensiveevaluation by the subjects were relatively dependent on D_(uv) values oftest light at the position of the illuminated object (according to theillumination method of the present invention) or test light emitted inthe main radiant direction from the light-emitting device (according tothe light-emitting device of the present invention), Tables 2 to 7 havebeen sorted in a descending order of D_(uv) values.

Overall, it was determined by the present experiment that the objectappearance or the color appearance of an actually observed object beingilluminated by test light is more favorable than when being illuminatedby experimental reference light if D_(uv) takes an appropriate negativevalue and |Δh_(n)|,

$\begin{matrix}\left\lbrack {{Expression}\mspace{14mu} 17} \right\rbrack & \; \\{\frac{\sum\limits_{n = 1}^{15}{\Delta \; C_{n}}}{15},} & \;\end{matrix}$

ΔC_(n), (|ΔC_(max)−ΔC_(min)|), and the like are within appropriateranges or if the index A_(cg) and the like are within appropriateranges. This result was unexpected in view of “results based oncurrently prevailing wisdom” described in step 1.

TABLE 2 Table 2: Summary of Experiment A (results of visual experimentand various indices) Light- emitting element CCT (K) D_(uv) |Δh_(n)|maxi- mum value |Δh_(n)| mini- mum value$\frac{\sum\limits_{n - 1}^{15}\; {\Delta \; C_{n}}}{15}$ ΔC_(max)ΔC_(min) |ΔC_(max) − ΔC_(min)| A_(cg) Luminous efficacy of radiation(lm/W) Ra Compre- hensive evaluation Reference Tungsten 2,589 −0.000230.20 0.02 0.07  0.30 −0.10  0.40 18.05 140 100 — light filamentIncandescent bulb (110 V) Comparative Purple LED 2,559 −0.00169 6.140.01 0.45  3.50 −2.04  5.54 −2.04 240  97 0 test light 1 BAM BSS CASONTest light 1 Purple LED 2,548 −0.00516 8.22 0.20 1.95  9.41 −3.44 12.84−32.01 235  94 1 SBCA β-SiAlON CASON Test light 2 Purple LED 2,538−0.01402 6.90 0.00 4.39 13.90 −0.83 14.73 −41.70 229  92 4 SBCA β-SiAlONCASON

TABLE 3 Table 3: Summary of Experiment B (results of visual experimentand various indices) Light- emitting element CCT (K) D_(uv) |Δh_(n)|maxi- mum value |Δh_(n)| mini- mum value$\frac{\sum\limits_{n - 1}^{15}\; {\Delta \; C_{n}}}{15}$ ΔC_(max)ΔC_(min) |ΔC_(max) − ΔC_(min)| A_(cg) Luminous efficacy of radiation(lm/W) Ra Compre- hensive evaluation Reference Tungsten 2,679 −0.000100.10 0.00 0.03 0.14 −0.05  0.19 3.40 145 100 — light filamentIncandescent bulb (120 V) Comparative Purple LED 2,631 −0.00255 6.240.00 0.71 4.23 −1.91  6.14 20.42 239  97 0 test light 2 BAM BSS CASONTest light 3 Purple LED 2,672 −0.00464 7.02 0.08 1.32 6.08 −1.85  7.93−11.06 236  96 1 SBCA β-SiAlON CASON Test light 4 Purple LED 2,636−0.01299 8.32 0.04 3.50 13.41 −2.43 15.83 −63.83 229  95 4 SBCA β-SiAlONCASON Test light 5 Purple LED 2,668 −0.01803 7.23 0.10 4.68 14.47 −0.6715.14 −114.08 222  91 5 SBCA β-SiAlON CASON Test light 6 Purple LED2,628 −0.02169 7.42 0.40 5.09 16.84 −0.96 17.81 −126.42 216  90 4 SBCAβ-SiAlON CASON

TABLE 4 Table 4: Summary of Experiment C (results of visual experimentand various indices) Light- emitting element CCT (K) D_(uv) |Δh_(n)|maxi- mum value |Δh_(n)| mini- mum value$\frac{\sum\limits_{n - 1}^{15}\; {\Delta \; C_{n}}}{15}$ ΔC_(max)ΔC_(min) |ΔC_(max) − ΔC_(min)| A_(cg) Luminous efficacy of radiation(lm/W) Ra Compre- hensive evaluation Comparative Blue LED 2,811  0.01380 9.51 0.29 −6.42 −0.11 −18.50 18.39 142.46 322  91 −4 testlight 3 BSON SCASN Comparative Blue LED 2,788   0.00970 5.00 0.51 −3.490.05 −11.04 11.10 102.87 309  94 −2 test light 4 BSON SCASN ComparativeCommercially 2,880   0.00819 5.78 0.29 −3.33 −0.07 −8.02 7.95 211.76 294 92 −2 test light 5 available LED Comparative Blue LED 2,723   0.000201.84 0.00 0.51 3.47 −2.37 5.84 15.58 299  94 0 test light 6 BSON SCASNReference Tungsten 2,749 −0.00017 0.12 0.00 0.04 0.18 −0.08 0.26 16.59150 100 — light filament Incandescent bulb (130 V) Comparative PurpleLED 2,703 −0.00331 6.26 0.08 0.91 4.76 −1.78 6.53 22.48 238  97 0 testlight 7 BAM BSS CASON Test light 7 Purple LED 2.784 −0.00446 6.30 0.061.17 5.46 −1.92 7.37 −13.19 235  96 1 BAM BSS CASON Test light 8 PurpleLED 2,761 −0.00561 7.16 0.07 1.48 6.60 −2.16 8.76 −46.26 232  96 1 BAMBSS CASON Test light 9 Blue LED 2,751 −0.01060 5.22 0.28 2.79 8.47 −2.0210.49 −28.57 289  93 3 BSON SCASN Test light Purple LED 2,798 −0.019916.11 0.06 4.25 13.37 −0.63 14.01 −141.79 221  91 5 10 SBCA β-SiAlONCASON Test light Purple LED 2,803 −0.02141 7.56 0.30 4.82 14.26 −0.8415.10 −176.30 216  90 4 11 SBCA β-SiAlON CASON Test light Blue LED 2,736−0.02210 4.56 0.07 4.99 12.13 −0.97 13.11 −139.12 257  85 4 12 BSONSCASN Test light Blue LED 2,718 −0.02840 7.10 0.23 6.36 16.62 0.89 15.72−174.29 251  84 2 13 BSON SCASN Comparative Blue LED 2,711 −0.03880 7.830.84 7.42 20.26 0.49 19.77 −253.28 240  80 −1 test light 8 BSON SCASNComparative Blue LED 2,759 −0.04270 7.61 0.16 7.86 20.06 1.04 19.03−228.40 231  77 −2 test light 9 BSON SCASN Comparative Blue LED 2,792−0.04890 5.92 0.24 7.50 19.12 1.22 17.90 −267.67 227  70 −3 test light10 BSON SCASN

TABLE 5 Table 5: Summary of Experiment D (results of visual experimentand various indices) Light- emitting element CCT (K) D_(uv) |Δh_(n)|maxi- mum value |Δh_(n)| mini- mum value$\frac{\sum\limits_{n - 1}^{15}\; {\Delta \; C_{n}}}{15}$ ΔC_(max)ΔC_(min) |ΔC_(max) − ΔC_(min)| A_(cg) Luminous efficacy of radiation(lm/W) Ra Compre- hensive evalua- tion Comparative Blue LED 3,0050.01411 18.54 0.18 −5.95 4.13 −13.83 17.96 197.80 376 69 −4 test light11 YAG CASON Pseudo- Purple LED 2,973 0.00064 3.48 0.02 −0.04 1.49 −1.482.98 31.87 245 97 — reference BAN BSS light CASON Comparative Blue LED2,911 −0.00667 18.39 0.62 0.82 14.09 −11.10 25.20 61.34 330 72 −2 testlight 12 YAG CASON Test light 14 Purple LED 3,026 −0.00742 3.77 0.182.53 6.06 −0.15 6.21 −17.86 281 92 1 SBCA β-SiAlON CASON ComparativeBlue LED 3,056 −0.01276 16.81 0.95 1.79 16.35 −10.53 26.88 25.24 319 74−2 test light 13 YAG CASON Test light 15 Purple LED 2,928 −0.01742 5.870.33 4.15 10.17 0.10 10.07 −177.14 216 88 5 SBCA β-SiAlON CASONComparative Blue LED 3,249 −0.01831 15.98 1.15 2.37 17.15 −10.01 27.16−6.20 310 75 −2 test light 14 YAG CASON Test light 16 Purple LED 2,992−0.02498 7.63 0.33 4.86 13.54 −1.11 14.65 −247.50 210 88 3 SBCA β-SiAlONCASON Test light 17 Purple LED 3,001 −0.02525 7.66 0.34 4.88 13.55 −1.1414.69 −253.58 209 88 2 SBCA β-SiAlON CASON

TABLE 6 Table 6: Summary of Experiment E (results of visual experimentand various indices) Light- emitting element CCT (K) D_(uv) |Δh_(n)|maxi- mum value |Δh_(n)| mini- mum value$\frac{\sum\limits_{n - 1}^{15}\; {\Delta \; C_{n}}}{15}$ ΔC_(max)ΔC_(min) |ΔC_(max) − ΔC_(min)| A_(cg) Luminous efficacy of radiation(lm/W) Ra Compre- hensive evaluation Pseudo- Purple LED 3,866   0.000064.76 0.05 0.52 3.37 −2.13 5.50 −6.84 249 94 — reference SBCA β-SiAlONlight CASON Test light 18 Purple LED 3,673 −0.01302 2.86 0.04 2.32 5.16−0.20 5.36 −82.35 236 93 4 SBCA β-SiAlON CASON Test light 19 Purple LED4,072 −0.01666 1.97 0.10 2.69 4.63 0.60 4.03 −116.16 230 89 5 SBCAβ-SiAlON CASON Test light 20 Purple LED 3,631 −0.02102 3.29 0.11 3.386.72 0.53 6.19 −173.43 223 87 4 SBCA β-SiAlON CASON

TABLE 7 Table 7: Summary of Experiment F (results of visual experimentand various indices) Light- emitting element CCT (K) D_(uv) |Δh_(n)|maxi- mum value |Δh_(n)| mini- mum value$\frac{\sum\limits_{n - 1}^{15}\; {\Delta \; C_{n}}}{15}$ ΔC_(max)ΔC_(min) |ΔC_(max) − ΔC_(min)| A_(cg) Luminous efficacy of radiation(lm/W) Ra Compre- hensive evaluation Comparative Purple LED 5,4900.0073137 5.45 0.03 −0.07 2.20 −2.45 4.65 56.25 255 94 −2 test light 15SBCA β-SiAlON CASON Pseudo- Purple LED 5,451 −0.002917 4.50 0.02 0.072.21 −3.05 5.26 94.78 275 96 — reference BAM BSS CASON light Test lightPurple LED 5,484 −0.005339 3.32 0.02 1.61 3.19 0.03 3.16 −84.44 234 92 121 SBCA β-SiAlON CASON Test light Purple LED 5,538 −0.007788 2.95 0.101.91 3.94 0.58 3.36 −86.47 231 90 2 22 SBCA β-SiAlON CASON Test lightPurple LED 5,661 −0.009926 3.32 0.27 2.17 4.70 0.91 3.80 −114.17 229 882 23 SBCA β-SiAlON CASON Test light Purple LED 5,577 −0.012668 3.72 0.082.49 5.31 0.95 4.36 −136.35 226 86 4 24 SBCA β-SiAlON CASON Test lightPurple LED 5,504 −0.01499 4.05 0.07 2.76 5.79 0.99 4.81 −155.28 224 84 425 SBCA β-SiAlON CASON Test light Purple LED 5,531 −0.017505 4.53 0.063.04 6.48 0.93 5.55 −173.79 222 82 5 26 SBCA β-SiAlON CASON Test lightPurple LED 5,650 −0.020101 5.14 0.13 3.34 7.34 0.79 6.56 −180.73 220 794 27 SBCA β-SiAlON CASON Test light Purple LED 5,470 −0.026944 6.06 0.254.06 8.68 0.82 7.86 −239.07 214 73 2 28 SBCA β-SiAlON CASON Test lightPurple LED 5,577 −0.033351 6.98 0.17 4.73 10.23 0.67 9.56 −322.02 205 661 29 SBCA β-SiAlON CASON Comparative Purple LED 5,681 −0.038497 7.530.04 5.26 11.36 0.51 10.86 −419.02 194 61 −1 test light 16 SBCA β-SiAlONCASON Comparative Purple LED 5,509 −0.043665 7.95 0.39 5.74 12.04 0.3711.66 −486.05 189 56 −2 test light 17 SBCA β-SiAlON CASON

[Details of Fourth Step, Consideration]

Hereinafter, the experiment results will be considered. Moreover, thetest lights and comparative test lights in the tables may sometimes becollectively referred to as a “test light”. 1) When D_(uv) of test lightis on positive side of experimental reference light (or experimentalpseudo-reference light)

Tables 4, 5, and 7 include results in which the D_(uv) of test light ison the positive side of experimental reference light (or experimentalpseudo-reference light). From these results, it is found that thegreater the positive value of the D_(uv) of the test light, the lessfavorable the color appearance or the object appearance of theilluminated objects as judged by the subjects. A more specificdescription will be given below.

With respect to the appearance of an illuminated white object, thesubjects judged that the greater the positive value of D_(uv) the moreyellowish (greenish) the appearance and the greater a feeling ofstrangeness. With respect to the appearance of gray portions of theilluminated color checkers, the subjects judged that differences inlightness became less visible. Furthermore, the subjects pointed outthat characters in illuminated printed matter became more illegible.Moreover, with respect to the color appearances of various illuminatedchromatic colors, the subjects judged that the greater the positivevalue of the D_(uv) of the test light, the more unnatural and dull thecolor appearances as compared to when illuminated by experimentalreference light (or experimental pseudo-reference light). The subjectspointed out that the various illuminated exterior wall color sampleswere perceived as being extremely different from the same colors whenviewed outdoors, and their own skin colors also appeared unnatural andunhealthy. In addition, the subjects pointed out that differences incolor of petals of fresh flowers with similar and analogous colorsbecame less distinguishable and contours became less visible as comparedto when illuminated by experimental reference light.

Furthermore, it was found that these results were not noticeablydependent on the CCT of the test lights described in Tables 4, 5, and 7,and also were not noticeably dependent on the configuration of thelight-emitting elements (light-emitting materials) of the light-emittingdevice.

Since the greater the positive value of the D_(uv) of the test light,the lower the value of Ra as an overall trend, one could argue that someof the results described above were within a range predictable from thedetailed mathematical examination performed in step 1.

2) When D_(uv) of test light is on negative side of experimentalreference light (or experimental pseudo-reference light)

All of the Tables 2 to 7 include results in which the D_(uv) of testlight is on the negative side of experimental reference light (orexperimental pseudo-reference light). These results show that when theD_(uv) of the test light was in an appropriate negative range and thevarious indices in the tables were in appropriate ranges, the subjectsjudged the color appearance or the object appearance of the illuminatedobject to be slightly favorable, favorable, more favorable, extremelyfavorable, or dramatically favorable. On the other hand, it is alsoshown that even if the D_(uv) of the test light was in a similar range,the color appearance or the object appearance of the illuminated objectwas judged to be unfavorable when the various indices in the tables werenot in appropriate ranges as shown in Table 5.

Among the results described above, it was totally unexpected that thecolor appearance of an object illuminated by test light would be anatural and favorable color appearance and a favorable object appearanceas compared to being illuminated by experimental reference light (orexperimental pseudo-reference light) when the D_(uv) of the test lightwas in an appropriate negative range and the various indices in thetables were in appropriate ranges. Details of features pointed out bythe subjects were as follows.

With white objects, the subjects judged that yellowness (greenness) haddecreased and the objects appeared slightly white, white, more white,extremely white, or dramatically white in comparison to beingilluminated by experimental reference light (or experimentalpseudo-reference light) when the D_(uv) of the test light was in anappropriate negative range and the various indices in the tables were inappropriate ranges. It was also pointed out that the closer to anoptimum range, the more natural and more favorable the appearance. Thiswas a totally unexpected result.

Furthermore, with gray portions of the color checkers, the subjectsjudged that differences in lightness had slightly increased, increased,further increased, extremely increased, or dramatically increased incomparison to being illuminated by experimental reference light (orexperimental pseudo-reference light) when the D_(uv) of the test lightwas in an appropriate negative range and the various indices in thetables were in appropriate ranges. The subjects also pointed out thatthe closer to an optimum range, the more natural and the higher thevisibility of the appearance. This was a totally unexpected result.

In addition, with contours of achromatic color samples, the subjectsjudged that clearness had slightly increased, increased, furtherincreased, extremely increased, or dramatically increased in comparisonto being illuminated by experimental reference light (or experimentalpseudo-reference light) when the D_(uv) of the test light was in anappropriate negative range and the various indices in the tables were inappropriate ranges. The subjects also pointed out that the closer to anoptimum range, the more natural and the higher the visibility of theappearance. This was a totally unexpected result.

Furthermore, with characters in printed matter, the subjects judged thatlegibility had slightly increased, increased, further increased,extremely increased, or dramatically increased in comparison to beingilluminated by experimental reference light (or experimentalpseudo-reference light) when the D_(uv) of the test light was in anappropriate negative range and the various indices in the tables were inappropriate ranges. The subjects also pointed out that the closer to anoptimum range, the more natural and the higher the legibility of theappearance of characters. This was a totally unexpected result.

In addition, with the illuminated objects in various chromatic colors,the subjects judged that the color appearances of the illuminatedobjects had a slightly natural vividness, a natural vividness, a furthernatural vividness, an extremely natural vividness, or a dramaticallynatural vividness in comparison to being illuminated by experimentalreference light (or experimental pseudo-reference light) when the D_(uv)of the test light was in an appropriate negative range and the variousindices in the tables were inappropriate ranges. The subjects alsopointed out that the closer to an optimum range, the more natural andfavorable the color appearance. This was a totally unexpected result.

Furthermore, with the various exterior wall color samples, the subjectsjudged that the color appearances of the color samples were slightlyclose, close, further close, extremely close, or dramatically close totheir memories when seeing the color samples outdoors in comparison tobeing illuminated by experimental reference light (or experimentalpseudo-reference light) when the D_(uv) of the test light was in anappropriate negative range and the various indices in the tables were inappropriate ranges. The subjects also pointed out that the closer to anoptimum range, the more natural and favorable the color appearance,which more closely resembled their memories when seeing the colorsamples outdoors. This was a totally unexpected result.

In addition, with the color appearances of the skin of the subjectsthemselves (Japanese), the subjects judged that their skin appearedslightly natural, natural, further natural, extremely natural, ordramatically natural in comparison to being illuminated by experimentalreference light (or experimental pseudo-reference light) when the D_(uv)of the test light was in an appropriate negative range and the variousindices in the tables were in appropriate ranges. The subjects alsopointed out that the closer to an optimum range, the more natural,healthy, and favorable the color appearance. This was a totallyunexpected result.

Furthermore, with differences in colors of petals of fresh flowers withsimilar and analogous colors, the subjects judged that the differencesbecame slightly distinguishable, distinguishable, furtherdistinguishable, extremely distinguishable, or dramaticallydistinguishable in comparison to being illuminated by experimentalreference light (or experimental pseudo-reference light) when the D_(uv)of the test light was in an appropriate negative range and the variousindices in the tables were in appropriate ranges. The subjects alsopointed out that the greater the negative value of D_(uv) relative to anappropriate upper limit within the experiment range, the greater thedistinguishability. This was a totally unexpected result.

In addition, with various illuminated objects, the subjects judged thatcontours appeared slightly clearer, clear, further clear, extremelyclear, or dramatically cleared in comparison to being illuminated byexperimental reference light (or experimental pseudo-reference light)when the D_(uv) of the test light was in an appropriate negative rangeand the various indices in the tables were in appropriate ranges. Thesubjects also pointed out that the greater the negative value of D_(uv)relative to an appropriate upper limit within the experiment range, theclearer the appearance of the contours. This was a totally unexpectedresult.

Particularly since the greater the negative value of the D_(uv) of thetest light, the lower the value of Ra as an overall trend, one couldargue that these results were totally unexpected from the detailedmathematical examination performed in step 1. As shown in Tables 2 to 7,purely focusing on Ra values reveal that, for example, Ra of test lightscomprehensively judged to be “dramatically favorable” ranged from around82 and 91 despite the fact that there were a large number of test lightswith Ra of 95 or higher. In addition, the comparative visual experimentswere performed beyond the D_(uv) range described in ANSI C78.377-2008.Therefore, one can argue that the results described above represent anovel discovery of a perceptually favorable region related to the colorappearance of an illuminated object outside of a current common-senserecommended chromaticity range.

Furthermore, with the illumination method according to the firstembodiment of the present invention, it was shown that, in addition toD_(uv), the various indices described in Tables 2 to 7 or, in otherwords, |Δh_(n)|,

$\begin{matrix}\left\lbrack {{Expression}\mspace{14mu} 18} \right\rbrack & \; \\{\frac{\sum\limits_{n = 1}^{15}{\Delta \; C_{n}}}{15},} & \;\end{matrix}$

ΔC_(n), and (|ΔC_(max)−ΔC_(min)|) must be within appropriate ranges inorder to obtain such perceptions. In addition, it was found that theindex A_(cg) and the luminous efficacy of radiation K (lm/W) arefavorably within appropriate ranges.

In particular, from the results of the test lights judged to befavorable in the visual experiments, in consideration of thecharacteristics of |Δh_(n)|,

$\begin{matrix}\left\lbrack {{Expression}\mspace{14mu} 19} \right\rbrack & \; \\{\frac{\sum\limits_{n = 1}^{15}{\Delta \; C_{n}}}{15},} & \;\end{matrix}$

ΔC_(n), and (|ΔC_(max)−ΔC_(min)|), it was found that the followingtrends exist. Specifically, test lights which produced a favorable colorappearance or a favorable object appearance had the followingcharacteristics with respect to the color appearance of the 15 colorsamples when illumination by calculational reference light is assumedand the color appearance of the 15 color samples when illumination by anactually measured test light spectral power distribution is assumed.

The difference in hue angles (Δh_(n)|) of the 15 color samples betweenillumination by test lights and illumination by calculational referencelight is relatively small, and an average saturation

$\begin{matrix}\left\lbrack {{Expression}\mspace{14mu} 20} \right\rbrack & \; \\\frac{\sum\limits_{n = 1}^{15}{\Delta \; C_{n}}}{15} & \;\end{matrix}$

of the 15 color samples when illuminated by the test lights hadincreased in an appropriate range as compared to that when illuminatedby the calculational reference light. Moreover, in addition to theaverage values, individual saturations (ΔC_(n)) of the 15 color samplesalso show that none of the respective ΔC_(n) of the 15 color sampleswhen illuminated by the test lights was excessively lower or higher thanthe same values when illuminated by the calculational reference lightand were all in appropriate ranges. As a result, the difference amongdifferences between maximum and minimum degrees of saturation(|ΔC_(max)−ΔC_(min)|) was narrow in an appropriate range. When furthersimplified, it is inferable that an ideal case features smalldifferences in hue angles among the hues of all 15 color samples and arelatively uniform increase in saturation of the 15 color samples withinappropriate ranges when assuming illumination by test light as comparedto when assuming illumination of the 15 color samples by referencelight.

A solid line in FIG. 35 represents a normalized test light spectralpower distribution of test light 5 judged to be “dramatically favorable”in the comprehensive judgment shown in Table 3. In addition, a dottedline in FIG. 35 represents a normalized spectral power distribution ofcalculational reference light (black-body radiator) calculated based ona CCT of the test light. On the other hand, FIG. 36 represents a CIELABplot related to color appearances of the 15 color samples when assumingillumination by the test light 5 (solid line) and assuming illuminationby the calculational reference light (black-body radiator) (dottedline). Moreover, while a direction perpendicular to the plane of paperrepresents lightness, only a* and b* axes were plotted for the sake ofconvenience.

Furthermore, FIGS. 37 and 38 summarize results of test light 15 judgedto be “dramatically favorable” in the comprehensive judgment shown inTable 5 in a similar manner to that described above, and FIGS. 39 and 40summarize results of test light 19 judged to be “dramatically favorable”in the comprehensive judgment shown in Table 6 in a similar manner tothat described above.

In this manner, it is shown that when a favorable color appearance or afavorable object appearance is obtained in the visual experiments,differences in hue angles among the hues of all 15 color samples aresmall and saturation of the 15 color samples increase relativelyuniformly within appropriate ranges when assuming illumination by thetest light as compared to when assuming illumination of the 15 colorsamples by the reference light. It is also shown that, from thisperspective, a CCT in a vicinity of 4000 K is favorable.

On the other hand, even if D_(uv) has a negative value in an appropriaterange, for example, comparative test light 14 with D_(uv)≅−0.01831 inTable 5 is judged in the visual experiments to have an unfavorableappearance created by the test lights. This is conceivably due to thefact that some characteristics among |Δh_(n)|,

$\begin{matrix}\left\lbrack {{Expression}\mspace{14mu} 21} \right\rbrack & \; \\{\frac{\sum\limits_{n = 1}^{15}{\Delta \; C_{n}}}{15},} & \;\end{matrix}$

ΔC_(n), and (|ΔC_(max)−ΔC_(min)|) were inappropriate. FIGS. 41 and 42represent a result of a CIELAB plot performed with respect to anormalized spectral power distribution and color appearances of the 15color samples for the comparative test light 14 in a similar manner toFIGS. 35, 36, and the like. As is apparent from FIGS. 41 and 42, thereis a large difference in hue angles among several hues of the 15 colorsamples and saturation of the 15 color samples vary in an extremelynon-uniform manner when comparing a case where illumination of the 15color samples by the reference light is assumed with a case whereillumination by the test lights is assumed.

The results of the visual experiments and the consideration thereof showthat the respective quantitative indices favorably fall within thefollowing ranges.

D_(uv) in the illumination method according to the first embodiment ofthe present invention was −0.0040 or lower, slightly favorably −0.0042or lower, favorably −0.0070 or lower, more favorably −0.0100 or lower,extremely favorably −0.0120 or lower, and dramatically favorably −0.0160or lower.

In addition, D_(uv) in the illumination method according to the firstembodiment of the present invention was −0.0350 or higher, slightlyfavorably −0.0340 or higher, favorably −0.0290 or higher, more favorably−0.0250 or higher, extremely favorably −0.0230 or higher, anddramatically favorably −0.0200 or higher.

Each |Δh_(n)| in the illumination method according to the firstembodiment of the present invention was 9.0 or lower, extremelyfavorably 8.4 or lower, and dramatically favorably 7.3 or lower. Inaddition, it is conceivable that a lower |Δh_(n)| is more favorable andthat each |Δh_(n)| is more dramatically favorably 6.0 or lower, furtherdramatically favorably 5.0 or lower, and particularly dramaticallyfavorably 4.0 or lower.

Moreover, each |Δh_(n)| in the illumination method according to thefirst embodiment of the present invention was 0 or higher and a minimumvalue thereof during the visual experiments was 0.0029. Furthermore, anexamination performed using actual test light during the visualexperiments revealed that a favorable range of each |Δh_(n)| withinfavorable experiment results under examination was 8.3 or lower and0.003 or higher.

$\begin{matrix}\left\lbrack {{Expression}\mspace{14mu} 22} \right\rbrack & \; \\\frac{\sum\limits_{n = 1}^{15}{\Delta \; C_{n}}}{15} & \;\end{matrix}$

in the illumination method according to the first embodiment of thepresent invention was: 1.0 or higher, slightly favorably 1.1 or higher,favorably 1.9 or higher, extremely favorably 2.3 or higher, anddramatically favorably 2.6 or higher; and

7.0 or lower, favorably 6.4 or lower, extremely favorably 5.1 or lower,and dramatically favorably 4.7 or lower.

Furthermore, an examination performed using actual test light during thevisual experiments revealed that a favorable range of the above indexwithin favorable experiment results under examination was 1.2 or higherand 6.3 or lower.

Each ΔC_(n) in the illumination method according to the first embodimentof the present invention was −3.8 or higher, slightly favorably −3.5 orhigher, extremely favorably −2.5 or higher, and dramatically favorably−0.7 or higher.

In addition, each ΔC_(n) in the illumination method according to thefirst embodiment of the present invention was 18.6 or lower, extremelyfavorably 17.0 or lower, and dramatically favorably 15.0 or lower.Furthermore, an examination performed using actual test light during thevisual experiments revealed that a favorable range of each ΔC_(n) withinfavorable experiment results under examination was −3.4 or higher and16.8 or lower.

While (|ΔC_(max)−ΔC_(min)|) in the illumination method according to thefirst embodiment of the present invention was 19.6 or lower,(|ΔC_(xax)−ΔC_(min)|) was extremely favorably 17.9 or lower, anddramatically favorably 15.2 or lower. In addition, it is conceivablethat a lower (|ΔC_(max)−ΔC_(min)|) is more favorable and that(|ΔC_(max)−ΔC_(min)|) is more dramatically favorably 14.0 or lower andextremely dramatically favorably 13.0 or lower.

Moreover, (|ΔC_(max)−ΔC_(min)|) in the illumination method according tothe first embodiment of the present invention was 2.8 or higher and aminimum value thereof during the visual experiments was 3.16.Furthermore, an examination performed using actual test light during thevisual experiments revealed that a favorable range of(|ΔC_(max)−ΔC_(min)|) within favorable experiment results underexamination was 3.2 or higher and 17.8 or lower.

Meanwhile, an attempt was made using Tables 2 to 7 to have a radiometricproperty and a photometric property of a test light spectral powerdistribution represent characteristics associated with test lights whichhad been comprehensively judged to have favorable characteristics in thevisual experiments.

Again, D_(uv) was as considered heretofore and was −0.0040 or lower,slightly favorably −0.0042 or lower, favorably −0.0070 or lower, morefavorably −0.0100 or lower, extremely favorably −0.0120 or lower, anddramatically favorably −0.0160 or lower.

In addition, D_(uv) according to the present invention was −0.0350 orhigher, slightly favorably −0.0340 or higher, favorably −0.0290 orhigher, more favorably −0.0250 or higher, extremely favorably −0.0230 orhigher, and dramatically favorably −0.0200 or higher.

On the other hand, the following observation was made regarding theindex A_(cg).

From results shown in Tables 2 to 7, A_(cg) in favorable spectral powerdistributions in the illumination method according to the firstembodiment of the present invention was −10 or lower and −360 or higher.Although a precise definition of A_(cg) is as described earlier, a roughphysical meaning or a clear interpretation thereof is as follows.“A_(cg) assumes a negative value in an appropriate range” means thatthere are appropriate existence of a concave and/or a convex shape in anormalized test light spectral power distribution, and radiant fluxintensity of the normalized test light spectral power distribution tendsto be higher than that of a mathematical normalized reference lightspectral power distribution in a short wavelength range between 380 nmand 495 nm, and/or radiant flux intensity of the normalized test lightspectral power distribution tends to be lower than that of amathematical normalized reference light spectral power distribution inan intermediate wavelength range between 495 nm and 590 nm, and/orradiant flux intensity of the normalized test light spectral powerdistribution tends to be higher than that of a mathematical normalizedreference light spectral power distribution in a long wavelength rangebetween 590 nm and Λ4. Since A_(cg) is a sum of respective elements inthe short wavelength range, the intermediate wavelength range, and thelong wavelength range, individual elements may not necessarily exhibitthe tendencies described above. Based on the above, it is understoodthat a favorable color appearance or a favorable object appearance wasproduced when A_(cg) is quantitatively −10 or lower and −360 or higher.

A_(cg) in the illumination method according to the first embodiment ofthe present invention was preferably −10 or lower, slightly favorably−11 or lower, more favorably −28 or lower, extremely favorably −41 orlower, and dramatically favorably −114 or lower.

In addition, in the illumination method according to the firstembodiment of the present invention, A_(cg) was preferably −360 orhigher, slightly favorably −330 or higher, favorably −260 or higher,extremely favorably −181 or higher, and dramatically favorably −178 orhigher.

Moreover, an examination performed using actual test light during thevisual experiments revealed that a favorable range of A_(cg) withinfavorable experiment results under examination was −322 or higher and−12 or lower.

Furthermore, while the first embodiment of the present invention aimedfor the realization of test light with favorable color appearance andhigh efficiency, results regarding luminous efficacy of radiation K wereas follows.

The luminous efficacy of radiation of the spectral power distributionsproduced by the illumination method according to the first embodiment ofthe present invention favorably ranged from 180 (lm/W) to 320 (lm/W) andwas at least higher by 20% or more than 150 (lm/W) which is a value ofan ordinary incandescent bulb or the like. This is conceivably due toinherence of radiation from a semiconductor light-emitting element orradiation from a phosphor and, at the same time, an appropriate concaveand/or convex shape was present at an appropriate position in thespectral power distributions with respect to a relationship with V (λ).From the perspective of achieving a balance with color appearance, theluminous efficacy of radiation in the illumination method according tothe present invention favorably ranged as described below.

Although the luminous efficacy of radiation K in the illumination methodaccording to the first embodiment of the present invention waspreferably 180 (lm/W) or higher, the luminous efficacy of radiation Kwas slightly favorably 205 (lm/W) or higher, favorably 208 (lm/W) orhigher, and extremely favorably 215 (lm/W) or higher. On the other hand,while, ideally, the higher the luminous efficacy of radiation K, thebetter, the luminous efficacy of radiation K in the present inventionwas preferably 320 (lm/W) or lower. In consideration of achieving abalance with color appearance, the luminous efficacy of radiation K wasslightly favorably 282 (lm/W) or lower, favorably 232 (lm/W) or lower,and dramatically favorably 231 (lm/W) or lower.

Moreover, an examination performed using actual test light during thevisual experiments revealed that a favorable range of K within favorableexperiment results under examination was 206 (lm/W) or higher and 288(lm/W) or lower.

Furthermore, the following findings were made regarding a CCT in theillumination method according to the first embodiment of the presentinvention. In order to have the various indices, namely, |Δh_(n)|,

$\begin{matrix}\left\lbrack {{Expression}\mspace{14mu} 23} \right\rbrack & \; \\{\frac{\sum\limits_{n = 1}^{15}{\Delta \; C_{n}}}{15},} & \;\end{matrix}$

ΔC_(n), and (|ΔC_(max)−ΔC_(min)|) assume more appropriate values whichwere judged as being favorable in the comparative visual experiments,CCT favorably assumed a value near 4000 K in the illumination methodaccording to the present invention. This is conceivably due to aspectral power distribution of light near 4000 K being hardly dependenton wavelength and is equi-energetic as also exhibited by referencelight, and a test light spectral power distribution in which a concaveand/or a convex shape is formed can be easily realized with respect toreference light. In other words, even in comparison to CCTs in othercases,

$\begin{matrix}\left\lbrack {{Expression}\mspace{14mu} 24} \right\rbrack & \; \\\frac{\sum\limits_{n = 1}^{15}{\Delta \; C_{n}}}{15} & \;\end{matrix}$

can be increased while keeping |Δh_(n) and (|ΔC_(max)−ΔC_(min)|) at lowlevels to easily control ΔC_(n) with respect to a large number of colorsamples so that each ΔC_(n) assumes a desired value.

Therefore, a CCT in the illumination method according to the firstembodiment of the present invention ranges slightly favorably from 1800K to 15000 K, favorably from 2000 K to 10000 K, more favorably from 2300K to 7000 K, extremely favorably from 2600 K to 6600 K, dramaticallyfavorably from 2900 K to 5800 K, and most favorably from 3400 K to 5100K.

Moreover, an examination performed using actual test light during thevisual experiments revealed that a favorable range of a CCT withinfavorable experiment results under examination was 2550 (K) or higherand 5650 (K) or lower.

Meanwhile, with the light-emitting device according to the secondembodiment of the present invention, it was shown that in order toobtain such perceptions, the indices A_(cg) described in Tables 2 to 7must be within appropriate ranges in addition to D_(uv). In addition, itwas revealed that the various indices, namely, the luminous efficacy ofradiation K (lm/W), |Δh_(n)|,

$\begin{matrix}\left\lbrack {{Expression}\mspace{14mu} 25} \right\rbrack & \; \\{\frac{\sum\limits_{n = 1}^{15}{\Delta \; C_{n}}}{15},} & \;\end{matrix}$

ΔC_(n), and (|ΔC_(max)−ΔC_(min)|) are favorably within appropriateranges.

Firstly, results of the test lights judged to be favorable in the visualexperiments revealed the following with respect to D_(uv) and the indexA_(cg).

First, D_(uv) was −0.0040 or lower, slightly favorably −0.0042 or lower,favorably −0.0070 or lower, more favorably −0.0100 or lower, extremelyfavorably −0.0120 or lower, and dramatically favorably −0.0160 or lower.

In addition, D_(uv) according to the present invention was −0.0350 orhigher, slightly favorably −0.0340 or higher, favorably −0.0290 orhigher, more favorably −0.0250 or higher, extremely favorably −0.0230 orhigher, and dramatically favorably −0.0200 or higher.

Furthermore, from results shown in Tables 2 to 7, λ_(c), in spectralpower distributions produced by the light-emitting device according tothe second embodiment of the present invention was −10 or lower and −360or higher. Although a precise definition of A_(cg) is as describedearlier, a rough physical meaning or a clear interpretation thereof isas follows. “A_(cg) assumes a negative value in an appropriate range”means that there are appropriate existence of a concave and/or a convexshape in a normalized test light spectral power distribution, andradiant flux intensity of the normalized test light spectral powerdistribution tends to be higher than that of a mathematical normalizedreference light spectral power distribution in a short wavelength rangebetween 380 nm and 495 nm, and/or radiant flux intensity of thenormalized test light spectral power distribution tends to be lower thanthat of a mathematical normalized reference light spectral powerdistribution in an intermediate wavelength range between 495 nm and 590nm, and/or radiant flux intensity of the normalized test light spectralpower distribution tends to be higher than that of a mathematicalnormalized reference light spectral power distribution in a longwavelength range between 590 nm and Λ4. Based on the above, it isunderstood that a favorable color appearance or a favorable objectappearance was produced when A_(cg) is quantitatively −10 or lower and−360 or higher.

A_(cg) as derived from a spectral power distribution of light emitted ina main radiant direction from the light-emitting device according to thesecond embodiment of the present invention was −10 or lower, slightlyfavorably −11 or lower, more favorably −28 or lower, extremely favorably−41 or lower, and dramatically favorably −114 or lower.

In addition, A_(cg) as derived from a spectral power distribution oflight emitted in a main radiant direction from the light-emitting deviceaccording to the second embodiment of the present invention was −360 orhigher, slightly favorably −330 or higher, favorably −260 or higher,extremely favorably −181 or higher, and dramatically favorably −178 orhigher.

Moreover, an examination performed using actual test light during thevisual experiments revealed that a favorable range of A_(cg) withinfavorable experiment results under examination was −322 or higher and−12 or lower.

Secondly, while the present invention aimed for the realization of testlight with favorable color appearance and high efficiency, resultsregarding luminous efficacy of radiation K were as follows.

The luminous efficacy of radiation of the spectral power distributionproduced by the light-emitting device according to the second embodimentof the present invention favorably ranged from 180 (lm/W) to 320 (lm/W)and was at least higher by 20% or more than 150 (lm/W) which is a valueof an ordinary incandescent bulb or the like. This is conceivably due toinherence of radiation from a semiconductor light-emitting element orradiation from a phosphor and, at the same time, an appropriate concaveand/or convex shape was present at an appropriate position in thespectral power distributions with respect to a relationship with V (λ).From the perspective of achieving a balance with color appearance, theluminous efficacy of radiation as obtained from a spectral powerdistribution of light emitted in a main radiant direction by thelight-emitting device according to the second embodiment of the presentinvention favorably ranged as described below.

Although the luminous efficacy of radiation K produced by thelight-emitting device according to the second embodiment of the presentinvention was preferably 180 (lm/W) or higher, the luminous efficacy ofradiation K was slightly favorably 205 (lm/W) or higher, favorably 208(lm/W) or higher, and extremely favorably 215 (lm/W) or higher. On theother hand, while, ideally, the higher the luminous efficacy ofradiation K, the better, the luminous efficacy of radiation K in thepresent invention was preferably 320 (lm/W) or lower. In considerationof achieving a balance with color appearance, the luminous efficacy ofradiation K was slightly favorably 282 (lm/W) or lower, favorably 232(lm/W) or lower, and dramatically favorably 231 (lm/W) of lower.

Moreover, an examination performed using actual test light during thevisual experiments revealed that a favorable range of K within favorableexperiment results under examination was 206 (lm/W) or higher and 288(lm/W) or lower.

Thirdly, when considering the characteristics of |Δh_(n)|,

$\begin{matrix}\left\lbrack {{Expression}\mspace{14mu} 26} \right\rbrack & \; \\{\frac{\sum\limits_{n = 1}^{15}{\Delta \; C_{n}}}{15},} & \;\end{matrix}$

ΔC_(n), and (|ΔC_(max)−ΔC_(min)|), it was found that the followingtrends exist. Specifically, test lights which produced a favorable colorappearance or a favorable object appearance had the followingcharacteristics with respect to the color appearance of the 15 colorsamples when illumination by calculational reference light is assumedand the color appearance of the 15 color samples when illumination by anactually measured test light spectral power distribution is assumed.

The difference in hue angles (|Δh_(n)|) of the 15 color samples betweenillumination by test lights and illumination by calculational referencelight is relatively small, and an average saturation

$\begin{matrix}\left\lbrack {{Expression}\mspace{14mu} 27} \right\rbrack & \; \\\frac{\sum\limits_{n = 1}^{15}{\Delta \; C_{n}}}{15} & \;\end{matrix}$

of the 15 color samples when illuminated by the test lights hadincreased in an appropriate range as compared to that when illuminatedby the calculational reference light. Moreover, in addition to theaverage values, individual saturations (ΔC_(n)) of the 15 color samplesalso show that none of the respective ΔC_(n) of the 15 color sampleswhen illuminated by the test lights was excessively lower or higher thanthe same values when illuminated by the calculational reference lightand were all in appropriate ranges. As a result, the difference amongdifferences between maximum and minimum degrees of saturation(|ΔC_(max)−ΔC_(min)|) was narrow in an appropriate range. When furthersimplified, it is inferable that an ideal case features smalldifferences in hue angles among the hues of all 15 color samples and arelatively uniform increase in saturation of the 15 color samples withinappropriate ranges when assuming illumination by test light as comparedto when assuming illumination of the 15 color samples by referencelight.

A solid line in FIG. 35 represents a normalized test light spectralpower distribution of the test light 5 judged to be “dramaticallyfavorable” in the comprehensive judgment shown in Table 3. In addition,a dotted line in FIG. 35 represents a normalized spectral powerdistribution of calculational reference light (black-body radiator)calculated based on a CCT of the test light. On the other hand, FIG. 36represents a CIELAB plot related to color appearances of the 15 colorsamples when assuming illumination by the test light 5 (solid line) andassuming illumination by the calculational reference light (black-bodyradiator) (dotted line). Moreover, while a direction perpendicular tothe plane of paper represents lightness, only a* and b* axes wereplotted for the sake of convenience.

Furthermore, FIGS. 37 and 38 summarize results of the test light 15judged to be “dramatically favorable” in the comprehensive judgmentshown in Table 5 in a similar manner to that described above, and FIGS.39 and 40 summarize results of the test light 19 judged to be“dramatically favorable” in the comprehensive judgment shown in Table 6in a similar manner to that described above.

In this manner, it is shown that when a favorable color appearance or afavorable object appearance is obtained in the visual experiments,differences in hue angles among the hues of all 15 color samples aresmall and saturation of the 15 color samples increase relativelyuniformly within appropriate ranges when assuming illumination by thetest light as compared to when assuming illumination of the 15 colorsamples by the reference light. It is also shown that, from thisperspective, a CCT in a vicinity of 4000 K is favorable.

On the other hand, even if D_(uv) has a negative value in an appropriaterange, for example, the comparative test light 14 with D_(uv)≅−0.01831in Table 5 is judged in the visual experiments to have an unfavorableappearance created by the test lights. This is conceivably due to thefact that characteristics of the index A_(cg), were not appropriate.FIGS. 41 and 42 represent a result of a CIELAB plot performed withrespect to a normalized spectral power distribution and colorappearances of the 15 color samples for the comparative test light 14 ina similar manner to FIGS. 35, 36, and the like. As is apparent fromFIGS. 41 and 42, there is a large difference in hue angles among severalhues of the 15 color samples and saturation of the 15 color samples varyin an extremely non-uniform manner when comparing a case whereillumination of the 15 color samples by the reference light is assumedwith a case where illumination by the test lights is assumed.

The results of the visual experiments and the consideration thereof showthat the respective quantitative indices favorably fall within thefollowing ranges.

As described earlier, D_(uv) in the light-emitting device according tothe second embodiment of the present invention was −0.0040 or lower,slightly favorably −0.0042 or lower, favorably −0.0070 or lower, morefavorably −0.0100 or lower, extremely favorably −0.0120 or lower, anddramatically favorably −0.0160 or lower.

In addition, D_(uv) in the light-emitting device according to the secondembodiment of the present invention was −0.0350 or higher, slightlyfavorably −0.0340 or higher, favorably −0.0290 or higher, more favorably−0.0250 or higher, extremely favorably −0.0230 or higher, anddramatically favorably −0.0200 or higher.

Each |Δh_(n)| in the light-emitting device according to the secondembodiment of the present invention was preferably 9.0 or lower,extremely favorably 8.4 or lower, and dramatically favorably 7.3 orlower. In addition, it is conceivable that a lower |Δh_(n)| is morefavorable and that each |Δh_(n)| is more dramatically favorably 6.0 orlower, further dramatically favorably 5.0 or lower, and particularlydramatically favorably 4.0 or lower.

Moreover, each |Δh_(n)| in the light-emitting device according to thesecond embodiment of the present invention was preferably 0 or higherand a minimum value thereof during the visual experiments was 0.0029.Furthermore, an examination performed using actual test light during thevisual experiments revealed that a favorable range of each |Δh_(n)|within favorable experiment results under examination was 8.3 or lowerand 0.003 or higher.

$\begin{matrix}\left\lbrack {{Expression}\mspace{14mu} 28} \right\rbrack & \; \\\frac{\sum\limits_{n = 1}^{15}{\Delta \; C_{n}}}{15} & \;\end{matrix}$

in the light-emitting device according to the second embodiment of thepresent invention was: preferably 1.0 or higher, slightly favorably 1.1or higher, favorably 1.9 or higher, extremely favorably 2.3 or higher,and dramatically favorably 2.6 or higher; and preferably 7.0 or lower,favorably 6.4 or lower, extremely favorably 5.1 or lower, anddramatically favorably 4.7 or lower.

Furthermore, an examination performed using actual test light during thevisual experiments revealed that a favorable range of the above indexwithin favorable experiment results under examination was 1.2 or higherand 6.3 or lower.

Each ΔC_(n) in the light-emitting device according to the secondembodiment of the present invention was preferably −3.8 or higher,slightly favorably −3.5 or higher, extremely favorably −2.5 or higher,and dramatically favorably −0.7 or higher.

In addition, each ΔC_(n) in the light-emitting device according to thesecond embodiment of the present invention was preferably 18.6 or lower,extremely favorably 17.0 or lower, and dramatically favorably 15.0 orlower.

Furthermore, an examination performed using actual test light during thevisual experiments revealed that a favorable range of each ΔC_(n) withinfavorable experiment results under examination was −3.4 or higher and16.8 or lower.

While (|ΔC_(max)−ΔC_(min)|) in the light-emitting device according tothe second embodiment of the present invention was preferably 19.6 orlower, (|ΔC_(max)−ΔC_(min)|) was extremely favorably 17.9 or lower, anddramatically favorably 15.2 or lower. In addition, it is conceivablethat a lower (|ΔC_(max)−ΔC_(min)|) is more favorable and that(|ΔC_(max)−ΔC_(min)|) is more dramatically favorably 14.0 or lower andextremely dramatically favorably 13.0 or lower.

Moreover, (|ΔC_(max)−ΔC_(min)|) in the light-emitting device accordingto the second embodiment of the present invention was preferably 2.8 orhigher and a minimum value thereof during the visual experiments was3.16. Furthermore, an examination performed using actual test lightduring the visual experiments revealed that a favorable range of(|ΔC_(max)−ΔC_(min)|) within favorable experiment results underexamination is 3.2 or higher and 17.8 or lower.

Fourthly, the following findings were made regarding a CCT in thelight-emitting device according to the second embodiment of the presentinvention. In order to have the various indices, namely, |Δh_(n)|,

$\begin{matrix}\left\lbrack {{Expression}\mspace{14mu} 29} \right\rbrack & \; \\{\frac{\sum\limits_{n = 1}^{15}{\Delta \; C_{n}}}{15},} & \;\end{matrix}$

ΔC_(n), and (|ΔC_(max)−ΔC_(min)|) assume more appropriate values whichwere judged as being favorable in the comparative visual experiments,CCT favorably assumed a value near 4000 K in the light-emitting deviceaccording to the second embodiment of the present invention. This isconceivably due to a spectral power distribution of light near 4000 Kbeing hardly dependent on wavelength and is equi-energetic as alsoexhibited by reference light, and a test light spectral powerdistribution in which a concave and/or a convex shape is formed can beeasily realized with respect to reference light. In other words, even incomparison to CCTs in other cases,

$\begin{matrix}\left\lbrack {{Expression}\mspace{14mu} 30} \right\rbrack & \; \\\frac{\sum\limits_{n = 1}^{15}{\Delta \; C_{n}}}{15} & \;\end{matrix}$

can be increased while keeping |Δh_(n) and (|ΔC_(max)−ΔC_(min)|) at lowlevels to easily control ΔC_(n) with respect to a large number of colorsamples so that each ΔC_(n) assumes a desired value.

Therefore, a CCT in the light-emitting device according to the secondembodiment of the present invention ranges slightly favorably from 1800K to 15000 K, favorably from 2000 K to 10000 K, more favorably from 2300K to 7000 K, extremely favorably from 2600 K to 6600 K, dramaticallyfavorably from 2900 K to 5800 K, and most favorably from 3400 K to 5100K.

Moreover, an examination performed using actual test light during thevisual experiments revealed that a favorable range of a CCT withinfavorable experiment results under examination was 2550 (K) or higherand 5650 (K) or lower.

While a favorable embodiment for implementing the illumination methodand the light-emitting device according to the present invention will bedescribed below, it is to be understood that modes for implementing theillumination method and the light-emitting device according to thepresent invention are not limited to those used in the followingdescription.

In the illumination method according to the present invention, norestrictions are placed on configurations, materials, and the like ofthe light-emitting device as long as a photometric property of testlight which is irradiated on an illuminated objects and which becomes acolor stimulus is in an appropriate range and, at the same time, adifference between color appearances of the 15 color samples whenillumination by calculational reference light is assumed and colorappearances of the 15 color samples when illumination by an actuallymeasured test light spectral power distribution is assumed is in anappropriate range.

With the light-emitting device according to the present invention, norestrictions are placed on configurations, materials, and the like ofthe light-emitting device as long as a radiometric property and aphotometric property of test light which is irradiated from thelight-emitting device in a main radiant direction and which becomes acolor stimulus with respect to an illuminated object are in appropriateranges.

A light-emitting device for implementing the illumination method or thelight-emitting device according to the present invention such as anillumination light source, a lighting fixture including the illuminationlight source, or a lighting system including the illumination lightsource or the lighting fixture includes at least one semiconductorlight-emitting element that is a light-emitting element. For example,the illumination light source including the semiconductor light-emittingelement may be configured such that a plurality of semiconductorlight-emitting elements of different types such as blue, green, and redis incorporated in one illumination light source or may be configuredsuch that a blue semiconductor light-emitting element is included in oneillumination light source, a green semiconductor light-emitting elementis included in another illumination light source, and a redsemiconductor light-emitting element is included in yet anotherillumination light source, whereby the semiconductor light-emittingelements are integrated with a lens, a reflecting mirror, a drivecircuit, and the like in a light fixture and provided to a lightingsystem. Furthermore, in a case where one illumination light source isincluded in one lighting fixture and an individual semiconductorlight-emitting element is incorporated in the illumination light source,even if the illumination method or the light-emitting device accordingto the present invention cannot be implemented as an individualillumination light source or an individual lighting fixture, a lightingsystem may be configured such that light radiated as the lighting systemsatisfies desired characteristics at a position of an illuminated objectdue to additive color mixing with light from a different lightingfixture that exists in the lighting system or the lighting system may beconfigured such that light in a main radiant direction among lightradiated as the lighting system satisfies desired characteristics. Inany mode, light as a color stimulus which is ultimately irradiated on anilluminated object or light in a main radiant direction among lightemitted from the light-emitting device need only satisfy appropriateconditions according to the present invention.

Hereinafter, characteristics will be described which are favorablyattained by a light-emitting device for implementing the illuminationmethod according to the first embodiment of the present invention or thelight-emitting device according to the second embodiment of the presentinvention on the basis of satisfying the appropriate conditionsdescribed above.

A light-emitting device for implementing the illumination methodaccording to the first embodiment of the present invention or thelight-emitting device according to the second embodiment of the presentinvention favorably includes a light-emitting element (light-emittingmaterial) which has a peak within a short wavelength range from Λ1 (380nm) to Λ2 (495 nm), another light-emitting element (light-emittingmaterial) which has a peak within an intermediate wavelength range fromΛ2 (495 nm) to Λ3 (590 nm), and yet another light-emitting element(light-emitting material) which has a peak within a long wavelengthrange from Λ3 (590 nm) to 780 nm. This is because favorable colorappearance can be readily achieved if intensity of each of thelight-emitting elements can be individually set or controlled.

Therefore, a light-emitting device for implementing the illuminationmethod according to the first embodiment of the present invention or thelight-emitting device according to the second embodiment of the presentinvention favorably includes at least one each of light-emittingelements (light-emitting materials) which have emission peaks in thethree respective wavelength ranges described above, more favorablyincludes one light-emitting element (light-emitting material) in each oftwo wavelength ranges among the three wavelength ranges and a pluralityof light-emitting elements (light-emitting materials) in the oneremaining wavelength range, extremely favorably includes onelight-emitting element (light-emitting material) in one wavelength rangeamong the three wavelength ranges and a plurality of light-emittingelements (light-emitting materials) in each of the two remainingwavelength ranges, and dramatically favorably includes a plurality oflight-emitting elements (light-emitting materials) in all threewavelength ranges. This is because by incorporating light-emittingelements such that two or more peak wavelengths exist in one range,controllability of a spectral power distribution dramatically increasesand, mathematically, a color appearance of an illuminated object can bemore readily controlled as desired.

Therefore, in an actual light-emitting device that uses a semiconductorlight-emitting element as a phosphor excitation light source, favorably,there are two types of phosphors in one light-emitting device and thereare peak wavelengths in each of the three wavelength ranges includingthe wavelength of the semiconductor light-emitting element. In addition,it is even more favorable to have three types of phosphors and have twolight-emitting elements incorporated in at least one range among thethree wavelength regions including the wavelength of the semiconductorlight-emitting element. From this perspective, it is extremely favorableto have four or more types of phosphors and dramatically favorable tohave five types of phosphors. In particular, if there are six or moretypes of phosphors in one light source, spectrum controllabilityinversely declines due to mutual absorption among the phosphors andtherefore becomes unfavorable. Furthermore, from a different perspectiveof realizing a simple light-emitting device, only one type of phosphormay be used and a light-emitting device may be configured with a totalof two types of light-emitting elements including an emission peak ofthe semiconductor light-emitting element.

This also applies to a case where an actual light-emitting device isconfigured using only semiconductor light-emitting elements withdifferent peak wavelengths. In other words, from the perspective ofrealizing a favorable spectral power distribution, the number ofdifferent types of semiconductor light-emitting elements in one lightsource is favorably three or more, more favorably four or more,extremely favorably five or more, and dramatically favorably six ormore. Having seven or more different types creates a hassle whenmounting on a light source or the like and therefore becomesunfavorable. Furthermore, from a different perspective of realizing asimple light-emitting device, a light-emitting device may be configuredwith two types of semiconductor light-emitting elements.

Moreover, semiconductor light-emitting elements and phosphors can bemixed and mounted at will. For example, a blue light-emitting elementand two types of phosphors (green and red) may be mounted in one lightsource, or a blue light-emitting element and three types of phosphors(green, red 1, and red 2) may be mounted in one light source.Furthermore, a purple light-emitting element and four types of phosphors(blue, green, red 1, and red 2) may be mounted in one light source.Moreover, one light source may incorporate a portion mounted with a bluelight-emitting element and two types of phosphors (green and red) and aportion mounted with a purple light-emitting element and three types ofphosphors (blue, green, and red).

From the perspective of controlling intensity of peak portions orintensity of valleys between peaks or, in other words, the perspectiveof forming an appropriate concave and/or convex shape in a spectralpower distribution, light-emitting elements (light-emitting materials)in each of the three wavelength ranges favorably include at least onelight-emitting element with a relatively narrow band. Conversely, it isdifficult to form an appropriate concave and/or convex shape in aspectral power distribution using only light-emitting elements withwidths comparable to widths of the three respective wavelength ranges.Therefore, in the present invention, it is favorable to include at leastone relatively narrow band light-emitting element. However, morefavorably, two ranges among the three respective wavelength rangesinclude a relatively narrow band light-emitting element and, even morefavorably, all of the three respective wavelength ranges include arelatively narrow band light-emitting element. In this case, while arelatively narrow band light-emitting element may itself individuallyconstitute a light-emitting element in a given wavelength region, morefavorably, a plurality of types of relatively narrow band light-emittingelements exist in the wavelength region and, equally more favorably, arelatively narrow band light-emitting element and a relatively broadband light-emitting element coexist in the wavelength region.

Moreover, a “relatively narrow band” as used herein refers to afull-width at half-maximum of a light-emitting element (light-emittingmaterial) being equal to or less than 2/3 of 115 nm, 95 nm, and 190 nmwhich are respective range widths of the short wavelength range (380 nmto 495 nm), the intermediate wavelength range (495 nm to 590 nm), andthe long wavelength range (590 nm to 780 nm). In addition, among arelatively narrow band light-emitting element, a full-width athalf-maximum of the light-emitting element with respect to therespective range widths is favorably ½ or less, more favorably ⅓ orless, extremely favorably ¼ or less, and dramatically favorably ⅕ orless. Furthermore, since a narrow band spectrum that is excessivelynarrow may result in a case where desired characteristics cannot berealized unless a large number of different types of light-emittingelements are mounted in a light-emitting device, the full-width athalf-maximum is favorably 2 nm or more, more favorably 4 nm or more,extremely favorably 6 nm or more, and dramatically favorably 8 nm ormore.

From the perspective of realizing a desired spectral power distribution,combining relatively narrow band light-emitting elements (light-emittingmaterials) is favorable since concave and/or a convex shape can be moreeasily formed in the spectral power distribution and the index A_(cg),the luminous efficacy of radiation K (lm/W), and the like whoseappropriate ranges have become apparent through the visual experimentscan be more easily set to desired values. In addition, it is favorableto treat light as a color stimulus and incorporate a relatively narrowband light-emitting element among the light-emitting elements since adifference between color appearances of the 15 color samples whenillumination by the light-emitting device is assumed and colorappearances when illumination by calculational reference light isassumed can be more conveniently used to perform saturation control and,in particular, to set |Δh_(n)|,

$\begin{matrix}\left\lbrack {{Expression}\mspace{14mu} 31} \right\rbrack & \; \\{\frac{\sum\limits_{n = 1}^{15}{\Delta \; C_{n}}}{15},} & \;\end{matrix}$

ΔC_(n), (|ΔC_(max)−ΔC_(min)|), and the like whose appropriate rangeshave become apparent through the visual experiments within appropriatenumerical value ranges. Furthermore, it is favorable to use a relativelynarrow band phosphor since D_(uv) control can be performed more easilythan when using a broad band phosphor.

In the illumination method and the light-emitting device according tothe present invention, the following light-emitting materials, phosphormaterials, and semiconductor light-emitting elements are favorablyincorporated in the light-emitting device as light-emitting elements.

First, in the short wavelength range from Λ1 (380 nm) to Λ2 (495 nm)among the three wavelength ranges, light emitted from all light sourcescan be included, such as thermal emission light from a hot filament orthe like, electric discharge emission light from a fluorescent tube, ahigh-pressure sodium lamp, or the like, stimulated emission light from alaser or the like, spontaneous emission light from a semiconductorlight-emitting element, and spontaneous emission light from a phosphor.Among the above, emission of light from a photoexcited phosphor,emission of light from a photoexcited semiconductor light-emittingelement, and emission of light from a photoexcited semiconductor laserare favorable due to their small sizes, high energy efficiency, andtheir ability to emit light in a relatively narrow band.

Specifically, the following is favorable.

Favorable examples of a semiconductor light-emitting element include apurple light-emitting element (with a peak wavelength of around 395 nmto 420 nm), a bluish purple light-emitting element (with a peakwavelength of around 420 nm to 455 nm), or a blue light-emitting element(with a peak wavelength of around 455 nm to 485 nm) in which anIn(Al)GaN material formed on a sapphire substrate or a GaN substrate isincluded in an active layer structure. Furthermore, a bluelight-emitting element (with a peak wavelength of around 455 nm to 485nm) in which a Zn(Cd) (S)Se material formed on a GaAs substrate isincluded in an active layer structure is also favorable.

Moreover, a spectral power distribution or a peak wavelength of aradiant flux produced by a light-emitting element (light-emittingmaterial) such as a semiconductor light-emitting element or a phosphornormally fluctuates slightly depending on ambient temperature, a heatdissipation environment of the light-emitting device including a packageand a fixture, injected current, circuit architecture and, in somecases, deterioration or the like. Therefore, a semiconductorlight-emitting element with a peak wavelength of 418 nm under a certaindrive condition may exhibit a peak wavelength of, for example, 421 nmwhen temperature of ambient environment rises.

The same applies to a spectral power distribution or a peak wavelengthof a radiant flux produced by light-emitting elements (light-emittingmaterials) such as the semiconductor light-emitting elements andphosphors described below.

The active layer structure may be any of a multiple quantum wellstructure in which a quantum well layer and a barrier layer arelaminated, a single or a double heterostructure including a relativelythick active layer and a barrier layer (or a clad layer), and a homojunction constituted by a single pn junction.

In particular, when the active layer includes an In(Al)GaN material, abluish purple light-emitting element and a purple light-emitting elementin which In concentration decreases in the active layer structure ascompared to a blue light-emitting element are favorable since emissionwavelength fluctuation due to segregation by In decreases and afull-width at half-maximum of the emission spectrum becomes narrower. Inaddition, a bluish purple light-emitting element and a purplelight-emitting element are favorable because wavelengths are positionedcloser to a relatively outer side (short wavelength-side) of thewavelength range from 380 nm to 495 nm and D_(uv) can be readilycontrolled. In other words, a semiconductor light-emitting elementhaving an emission peak in the short wavelength range from Λ1 (380 nm)to Λ2 (495 nm) in the present invention is favorably a bluelight-emitting element (with a peak wavelength of around 455 nm to 485nm), more favorably a bluish purple light-emitting element (with a peakwavelength of around 420 nm to 455 nm) with a shorter wavelength, andextremely favorably a purple light-emitting element (with a peakwavelength of around 395 nm to 420 nm) with a shorter wavelength.Furthermore, it is also favorable to use a plurality of types of theselight-emitting elements.

Moreover, a semiconductor laser is also favorably used as thelight-emitting element and, for the same reasons as described above, thesemiconductor laser is favorably a blue semiconductor laser (with anemission wavelength of around 455 nm to 485 nm), more favorably a bluishpurple semiconductor laser (with an emission wavelength of around 420 nmto 455 nm) with a longer wavelength, and extremely favorably a purplesemiconductor laser (with an emission wavelength of around 395 nm to 420nm) with a longer wavelength.

With a short wavelength range semiconductor light-emitting element thatis used in the illumination method or the light-emitting deviceaccording to the present invention, a full-width at half-maximum of anemission spectrum of the semiconductor light-emitting element isfavorably narrow. From this perspective, the full-width at half-maximumof the semiconductor light-emitting element used in the short wavelengthrange is favorably 45 nm or less, more favorably 40 nm or less,extremely favorably 35 nm or less, and dramatically favorably 30 nm orless. On the other hand, since an excessively narrow band spectrum mayresult in a case where desired characteristics cannot be realized unlessa large number of different types of light-emitting elements are mountedin a light-emitting device, the full-width at half-maximum of thesemiconductor light-emitting element used in the short wavelength rangeis favorably 2 nm or more, more favorably 4 nm or more, extremelyfavorably 6 nm or more, and dramatically favorably 8 nm or more.

Since the short wavelength range semiconductor light-emitting elementthat is used in the illumination method or the light-emitting deviceaccording to the present invention favorably includes an In(Al)GaNmaterial in an active layer structure, the semiconductor light-emittingelement is favorably a light-emitting element formed on a sapphiresubstrate or a GaN substrate. In particular, the degree of Insegregation in the active layer of a light-emitting element formed on aGaN substrate is more favorable than when formed on a sapphiresubstrate. This is dependent on the degree of lattice matching betweenthe substrate and active layer structure material. Therefore, since thefull-width at half-maximum of an In(Al)GaN emission spectrum on a GaNsubstrate can be set narrower, a dramatic synergistic effect with thepresent invention can be expected and is therefore extremely favorable.Furthermore, even among light-emitting elements on a GaN substrate,elements formed on a semi-polar surface or a non-polar surface areparticularly favorable. This is because a decrease in a piezoelectricpolarization effect in a crystal growth direction causes an increase inspatial overlapping of electrons' and holes' wave function in a quantumwell layer and, in principle, an increase in radiation efficiency and anarrower band spectrum can be achieved. Therefore, by using asemiconductor light-emitting element on a semi-polar or non-polar GaNsubstrate, a dramatic synergistic effect with the present invention canbe expected and is therefore extremely favorable.

In addition, as far as substrate thickness is concerned, the substrateis favorably either thick or completely separated from the semiconductorlight-emitting element. In particular, when creating a short wavelengthrange semiconductor light-emitting element on a GaN substrate, in orderto facilitate light extraction from side walls of the GaN substrate, thesubstrate is favorably thick and is 100 μm or more, more favorably 200μm or more, extremely favorably 400 μm or more, and dramaticallyfavorably 600 μm or more. On the other hand, for convenience of creatingelements, the substrate thickness is favorably 2 mm or less, morefavorably 1.8 mm or less, extremely favorably 1.6 mm or less, anddramatically favorably 1.4 mm or less.

Meanwhile, when creating a light-emitting element on a sapphiresubstrate or the like, the substrate is favorably separated using amethod such as laser lift-off. Such a configuration reduces stressacting on the quantum well layer which facilitates widening of bandwidthdue to an extreme lattice mismatch with the substrate and, as a result,a narrower band spectrum of the light-emitting element can be achieved.Therefore, with a light-emitting element separated from a sapphiresubstrate or the like, a dramatic synergistic effect with the presentinvention can be expected and is therefore extremely favorable.

With a short wavelength range phosphor material that is used in theillumination method or the light-emitting device according to thepresent invention, a full-width at half-maximum of the phosphor materialis favorably narrow. From this perspective, the full-width athalf-maximum of an emission spectrum of the phosphor material used inthe short wavelength range when photoexcited at room temperature isfavorably 90 nm or less, more favorably 80 nm or less, extremelyfavorably 70 nm or less, and dramatically favorably 60 nm or less. Onthe other hand, since an excessively narrow band spectrum may result ina case where desired characteristics cannot be realized unless a largenumber of different types of light-emitting elements are mounted in alight-emitting device, the full-width at half-maximum of the phosphormaterial used in the short wavelength range is favorably 2 nm or more,more favorably 4 nm or more, extremely favorably 6 nm or more, anddramatically favorably 8 nm or more.

With a short wavelength range phosphor material, in consideration ofexciting the phosphor material and D_(uv) controllability, the phosphormaterial favorably has a peak wavelength in the following ranges. In acase of light excitation, the peak wavelength favorably ranges from 455nm to 485 nm and more favorably has a shorter wavelength from 420 nm to455 nm. On the other hand, in a case of electron beam excitation, thepeak wavelength favorably ranges from 455 nm to 485 nm, more favorablyhas a shorter wavelength from 420 nm to 455 nm, and extremely favorablyhas a shorter wavelength from 395 nm to 420 nm.

As for specific examples of the short wavelength range phosphor materialused in the illumination method or the light-emitting device accordingto the present invention, while any phosphor material satisfying thefull-width at half-maximum described above can be favorably used, onespecific example is a blue phosphor which uses Eu²⁺ as an activator anda crystal constituted by alkaline-earth aluminate or alkaline-earthhalophosphate as a host. More specifically, examples include a phosphorrepresented by the following general formula (5), a phosphor representedby the following general formula (5)′, (Sr, Ba)₃MgSi₂O₈:Eu²⁺, and(Ba,Sr,Ca, Mg)Si₂O₂N₂: Eu.

(Ba,Sr,Ca)MgAl₁₀O₁₇:Mn,Eu  (5)

(An alkaline-earth aluminate phosphor represented by the general formula(5) is referred to as a BAM phosphor).

Sr_(a)Ba_(b)Eu_(x)(PO₄)_(c)X_(d)  (5)′

(In the general formula (5)′, X is Cl. In addition, c, d, and x arenumbers satisfying 2.7≤c≤3.3, 0.9≤d≤1.1, and 0.3≤x≤1.2. Furthermore, aand b satisfy conditions represented by a+b=5−x and 0≤b/(a+b)≤0.6).(Among alkaline-earth halophosphate phosphors represented by generalformula (5)′, those containing Ba is referred to as SBCA phosphors andthose not containing Ba is referred to as SCA phosphors).

Favorable examples of such phosphors include a BAM phosphor, a SBCAphosphor, a SCA phosphor, a Ba-SION phosphor ((Ba,Sr,Ca,Mg)Si₂O₂N₂:Eu),and a (Sr, Ba)₃MgSi₂O₈:Eu²⁺ phosphor. Next, in the intermediatewavelength range from Λ2 (495 nm) to Λ3 (590 nm) among the threewavelength ranges, light emitted from all light sources can be included,such as thermal emission light from a hot filament or the like, electricdischarge emission light from a fluorescent tube, a high-pressure sodiumlamp, or the like, stimulated emission light from a laser or the likeincluding second-order harmonic generation (SHG) using a non-linearoptical effect or the like, spontaneous emission light from asemiconductor light-emitting element, and spontaneous emission lightfrom a phosphor. Among the above, emission of light from a photoexcitedphosphor, emission of light from a photoexcited semiconductorlight-emitting element, emission of light from a photoexcitedsemiconductor laser, and emission of light from a photoexcited SHG laserare favorable due to their small sizes, high energy efficiency, andtheir ability to emit light in a relatively narrow band.

Specifically, the following is favorable.

Favorable examples of a semiconductor light-emitting element include agreenish blue light-emitting element (with a peak wavelength of around495 nm to 500 nm), a green light-emitting element (with a peakwavelength of around 500 nm to 530 nm), a yellowish green light-emittingelement (with a peak wavelength of around 530 nm to 570 nm), or a yellowlight-emitting element (with a peak wavelength of around 570 nm to 580nm) in which an In(Al)GaN material on a sapphire substrate or a GaNsubstrate is included in an active layer structure. In addition, ayellowish green light-emitting element (with a peak wavelength of around530 nm to 570 nm) due to GaP on a GaP substrate or a yellowlight-emitting element (with a peak wavelength of around 570 nm to 580nm) due to GaAsP on a GaP substrate is also favorable. Furthermore, ayellow light-emitting element (with a peak wavelength of around 570 nmto 580 nm) due to AlInGaP on a GaAs substrate is also favorable.

The active layer structure may be any of a multiple quantum wellstructure in which a quantum well layer and a barrier layer arelaminated, a single or a double heterostructure including a relativelythick active layer and a barrier layer (or a clad layer), and a homojunction constituted by a single pn junction.

In particular, when using an In (Λ1)GaN material, a yellowish greenlight-emitting element, a green light-emitting element, and a greenishblue light-emitting element in which In concentration decreases in theactive layer structure as compared to a yellow light-emitting elementare favorable since emission wavelength fluctuation due to segregationby In decreases and a full-width at half-maximum of the emissionspectrum becomes narrower. In other words, a semiconductorlight-emitting element having an emission peak in the intermediatewavelength range from Λ2 (495 nm) to Λ3 (590 nm) in the presentinvention is favorably a yellow light-emitting element (with a peakwavelength of around 570 nm to 580 nm), more favorably a yellowish greenlight-emitting element (with a peak wavelength of around 530 nm to 570nm) with a shorter wavelength, extremely favorably a greenlight-emitting element (with a peak wavelength of around 500 nm to 530nm) with a shorter wavelength, and dramatically favorably a greenishblue light-emitting element (with a peak wavelength of around 495 nm to500 nm).

Furthermore, a semiconductor laser, an SHG laser which converts anemission wavelength of a semiconductor laser using a non-linear opticaleffect, and the like are also favorably used as a light-emittingelement. For the same reasons as described above, an emission wavelengthis favorably within a yellow range (with a peak wavelength of around 570nm to 580 nm), more favorably within a yellowish green range (with apeak wavelength of around 530 nm to 570 nm) with a shorter wavelength,extremely favorably within a green range (with a peak wavelength ofaround 500 nm to 530 nm) with a shorter wavelength, and dramaticallyfavorably within a greenish blue range (with a peak wavelength of around495 nm to 500 nm).

With an intermediate wavelength range semiconductor light-emittingelement that is used in the illumination method or the light-emittingdevice according to the present invention, a full-width at half-maximumof an emission spectrum of the semiconductor light-emitting element isfavorably narrow. From this perspective, the full-width at half-maximumof the semiconductor light-emitting element used in the intermediatewavelength range is favorably 75 nm or less, more favorably 60 nm orless, extremely favorably 50 nm or less, and dramatically favorably 40nm or less. On the other hand, since an excessively narrow band spectrummay result in a case where desired characteristics cannot be realizedunless a large number of different types of light-emitting elements aremounted in a light-emitting device, the full-width at half-maximum ofthe semiconductor light-emitting element used in the intermediatewavelength range is favorably 2 nm or more, more favorably 4 nm or more,extremely favorably 6 nm or more, and dramatically favorably 8 nm ormore.

When the intermediate wavelength range semiconductor light-emittingelement that is used in the present invention includes an In(Al)GaNmaterial in an active layer structure, the semiconductor light-emittingelement is favorably a light-emitting element formed on a sapphiresubstrate or a GaN substrate. In addition, a light-emitting elementformed on a GaN substrate is particularly favorable. This is due to thefact that while In must be introduced into the active layer structure ina relatively large amount when creating an InAlGaN element in theintermediate wavelength range, an InAlGaN element formed on a GaNsubstrate reduces a piezoelectric effect attributable to a difference inlattice constants from the substrate and enables suppression of spatialseparation of electrons/holes when injecting a carrier into a quantumwell layer as compared to an InAlGaN element formed on a sapphiresubstrate. As a result, a full-width at half-maximum of the emissionwavelength can be narrowed. Therefore, in the present invention, with anintermediate wavelength range semiconductor light-emitting element on aGaN substrate, a dramatic synergistic effect can be expected and istherefore favorable. Furthermore, even among light-emitting elements ona GaN substrate, elements formed on a semi-polar surface or a non-polarsurface are particularly favorable. This is because a decrease in apiezoelectric polarization effect in a crystal growth direction causesan increase in spatial overlapping of electrons' and holes' wavefunction in a quantum well layer and, in principle, an increase inluminous efficiency and a narrower band spectrum can be achieved.Therefore, by using a semiconductor light-emitting element on asemi-polar or non-polar GaN substrate, a dramatic synergistic effectwith the present invention can be expected and is therefore extremelyfavorable.

With all semiconductor light-emitting elements, regardless of the typeof substrate on which the semiconductor light-emitting element isformed, the substrate is favorably either thick or completely removed.

In particular, when creating an intermediate wavelength rangesemiconductor light-emitting element on a GaN substrate, in order tofacilitate light extraction from side walls of the GaN substrate, thesubstrate is favorably thick and is 100 m or more, more favorably 200 mor more, extremely favorably 400 μm or more, and dramatically favorably600 m or more. On the other hand, for convenience of creating elements,the substrate thickness is favorably 2 mm or less, more favorably 1.8 mmor less, extremely favorably 1.6 mmor less, and dramatically favorably1.4 mm or less.

In addition, the same applies when creating an intermediate wavelengthrange semiconductor light-emitting element on a GaP substrate and, inorder to facilitate light extraction from side walls of the GaPsubstrate, the substrate is favorably thick and is 100 μm or more, morefavorably 200 μm or more, extremely favorably 400 m or more, anddramatically favorably 600 pin or more. On the other hand, forconvenience of creating elements, the substrate thickness is favorably 2mm or less, more favorably 1.8 mm or less, extremely favorably 1.6 mm orless, and dramatically favorably 1.4 mm or less.

Meanwhile, in a case of an AlInGaP material formed on a GaAs substrate,light in the emission wavelength range is absorbed due to a bandgap ofthe substrate being smaller than a bandgap of the material constitutingthe active layer structure. Therefore, as far as substrate thickness isconcerned, the substrate is favorably thin or completely separated fromthe semiconductor light-emitting element.

In addition, when creating a light-emitting element on a sapphiresubstrate or the like, the substrate is favorably separated using amethod such as laser lift-off. Such a configuration reduces stressacting on the quantum well layer which causes widening of bandwidth dueto an extreme lattice mismatch with the substrate and, as a result, anarrower band spectrum of the light-emitting element can be achieved.Therefore, with a semiconductor light-emitting element separated from asapphire substrate or the like, a dramatic synergistic effect with thepresent invention can be expected and is therefore extremely favorable.

With an intermediate wavelength range phosphor material that is used inthe illumination method or the light-emitting device according to thepresent invention, a full-width at half-maximum of the phosphor materialis favorably narrow. From this perspective, the full-width athalf-maximum of an emission spectrum of the phosphor material used inthe intermediate wavelength range when photoexcited at room temperatureis favorably 130 nm or less, more favorably 110 nm or less, extremelyfavorably 90 nm or less, and dramatically favorably 70 nm or less. Onthe other hand, since an excessively narrow band spectrum may result ina case where desired characteristics cannot be realized unless a largenumber of different types of light-emitting elements are mounted in alight-emitting device, the full-width at half-maximum of the phosphormaterial used in the intermediate wavelength range is favorably 2 nm ormore, more favorably 4 nm or more, extremely favorably 6 nm or more, anddramatically favorably 8 nm or more.

With an intermediate wavelength range phosphor material, inconsideration of D_(uv) controllability, a peak wavelength of thephosphor material favorably ranges from 495 nm to 500 nm. A peakwavelength ranging from 500 nm to 530 nm and a peak wavelength rangingfrom 570 nm to 580 nm are both more favorable to similar degrees, and apeak wavelength ranging from 530 nm to 570 nm is extremely favorable.

As for specific examples of the intermediate wavelength range phosphormaterial used in the illumination method or the light-emitting deviceaccording to the present invention, any phosphor material satisfying thefull-width at half-maximum described above can be favorably used. Inaddition, such specific examples include a green phosphor containingEu²⁺, Ce³⁺, or the like as an activator. A preferable green phosphorusing Eu²⁺ as an activator is a green phosphor which uses a crystalconstituted by alkaline-earth silicate, alkaline-earth nitride silicate,or SiAlON as a host. A green phosphor of this type can normally beexcited using a semiconductor light-emitting element ranging fromultraviolet to blue.

Specific examples of those using an alkaline-earth silicate crystal as ahost include a phosphor represented by the following general formula (6)and a phosphor represented by the following general formula (6)′.

(Ba_(a)Ca_(b)Sr_(c)Mg_(d)Eu_(x))SiO₄  (6)

(In the general formula (6), a, b, c, d, and x satisfy a+b+c+d+x=2,1.0≤a≤2.0, 0≤b<0.2, 0.2≤c≤0.8, 0≤d≤0.2, and 0<x≤0.5). (Alkaline-earthsilicate represented by the general formula (6) is referred to as a BSSphosphor).

Ba_(1-x-y)Sr_(x)Eu_(y)Mg_(1-z)Mn_(z)Al₁₀O₁₇  (6)′

(In the general formula (6)′, x, y, and z respectively satisfy0.1≤x≤0.4, 0.25≤y≤0.6, and 0.05≤z≤0.5). (An alkaline-earth aluminatephosphor represented by general formula (6)′ is referred to as a G-BAMphosphor).

Specific examples having a SiAlON crystal as a host include a phosphorrepresented by Si_(6-z)Al_(z)O_(z)N_(8-z):Eu (where 0<z<4.2) (thisphosphor is referred to as a β-SiAlON phosphor). Preferable greenphosphors using Ce³⁺ as an activator include a green phosphor with agarnet-type oxide crystal as a host such as Ca₃(Sc,Mg)₂Si₃O₁₂:Ce or agreen phosphor with an alkaline-earth scandate crystal as a host such asCaSc₂O₄:Ce. Other examples include SrGaS₄:Eu²⁺.

Still other examples include an oxynitride phosphor represented by(Ba,Ca,Sr,Mg, Zn,Eu)₃Si₆O₁₂N₂ (this phosphor is referred to as a BSONphosphor).

Yet other examples include a yttrium aluminum garnet phosphorrepresented by (Y_(1-u)Gd_(u))₃(Al_(1-v)Ga_(v))₅O₁₂:Ce,Eu (where u and vrespectively satisfy 0≤u≤0.3 and 0≤v≤0.5) (this phosphor is referred toas a YAG phosphor) and a lanthanum silicon nitride phosphor representedby Ca_(1.5x)La_(3-x)Si₆N₁₁:Ce (where x satisfies 0≤x≤1) (this phosphoris referred to as an LSN phosphor).

Among the phosphors described above, favorable examples include a BSSphosphor, a β-SiAlON phosphor, a BSON phosphor, a G-BAM phosphor, a YAGphosphor, and a SrGaS₄:Eu²⁺ phosphor.

Next, in the long wavelength range from Λ3 (590 nm) to 780 nm among thethree wavelength ranges, light emitted from all light sources can beincluded, such as thermal emission light from a hot filament or thelike, electric discharge emission light from a fluorescent tube, ahigh-pressure sodium lamp, or the like, stimulated emission light from alaser or the like, spontaneous emission light from a semiconductorlight-emitting element, and spontaneous emission light from a phosphor.Among the above, emission of light from a photoexcited phosphor,emission of light from a photoexcited semiconductor light-emittingelement, and emission of light from a photoexcited semiconductor laserare favorable due to their small sizes, high energy efficiency, andtheir ability to emit light in a relatively narrow band.

Specifically, the following is favorable.

As the semiconductor light-emitting element, an orange light-emittingelement (with a peak wavelength of around 590 nm to 600 nm) or a redlight-emitting element (from 600 nm to 780 nm) in which an AlGaAsmaterial formed on a GaAs substrate or an (Al)InGaP material formed on aGaAs substrate is included in an active layer structure is favorable. Inaddition, a red light-emitting element (from 600 nm to 780 nm) in whichan GaAsP material formed on a GaP substrate is included in an activelayer structure is favorable.

The active layer structure may be any of a multiple quantum wellstructure in which a quantum well layer and a barrier layer arelaminated, a single or a double heterostructure including a relativelythick active layer and a barrier layer (or a clad layer), and a homojunction constituted by a single pn junction.

In particular, in this wavelength range, a peak wavelength is favorablyclose to a vicinity of 630 nm in consideration of achieving a balancebetween D_(uv) controllability and luminous efficacy of radiation. Fromthis perspective, a red light-emitting element is more favorable than anorange light-emitting element. In other words, a semiconductorlight-emitting element having an emission peak in the long wavelengthrange from Λ3 (590 nm) to 780 nm in the present invention is favorablyan orange light-emitting element (with a peak wavelength of around 590nm to 600 nm), more favorably a red light-emitting element (with a peakwavelength of around 600 nm to 780 nm), and extremely favorably a redlight-emitting element with a peak wavelength that is close to around630 nm. In particular, a red light-emitting element with a peakwavelength ranging from 615 nm to 645 nm is extremely favorable.

In addition, a semiconductor laser is also favorably used as alight-emitting element. For the same reasons as described above, anemission wavelength is favorably within an orange range (with a peakwavelength of around 590 nm to 600 nm), more favorably within a redrange (with a peak wavelength of around 600 nm to 780 nm), and extremelyfavorably within a red range in which a peak wavelength is close toaround 630 nm. In particular, a red semiconductor laser with a peakwavelength ranging from 615 nm to 645 nm is extremely favorable.

With a long wavelength range semiconductor light-emitting element thatis used in the illumination method or the light-emitting deviceaccording to the present invention, a full-width at half-maximum of anemission spectrum of the semiconductor light-emitting element isfavorably narrow. From this perspective, the full-width at half-maximumof the semiconductor light-emitting element used in the long wavelengthrange is favorably 30 nm or less, more favorably 25 nm or less,extremely favorably 20 nm or less, and dramatically favorably 15 nm orless. On the other hand, since an excessively narrow band spectrum mayresult in a case where desired characteristics cannot be realized unlessa large number of different types of light-emitting elements are mountedin a light-emitting device, the full-width at half-maximum of thesemiconductor light-emitting element used in the long wavelength rangeis favorably 2 nm or more, more favorably 4 nm or more, extremelyfavorably 6 nm or more, and dramatically favorably 8 nm or more.

In the long wavelength range, light in the emission wavelength range isabsorbed due to a bandgap of the GaAs substrate being smaller than abandgap of the material constituting the active layer structure.Therefore, as far as substrate thickness is concerned, the substrate isfavorably thin or completely removed.

With a long wavelength range phosphor material that is used in theillumination method or the light-emitting device according to thepresent invention, a full-width at half-maximum of the phosphor materialis favorably narrow. From this perspective, the full-width athalf-maximum of an emission spectrum of the phosphor material used inthe long wavelength range when photoexcited at room temperature isfavorably 130 nm or less, more favorably 110 nm or less, extremelyfavorably 90 nm or less, and dramatically favorably 70 nm or less. Onthe other hand, since an excessively narrow band spectrum may result ina case where desired characteristics cannot be realized unless a largenumber of different types of light-emitting elements are mounted in alight-emitting device, the full-width at half-maximum of the phosphormaterial used in the long wavelength range is favorably 2 nm or more,more favorably 4 nm or more, extremely favorably 6 nm or more, anddramatically favorably 8 nm or more.

With a long wavelength range phosphor material, when creating alight-emitting device by integrating the phosphor material with othermaterials, a peak wavelength is extremely favorably close to 630 nm inconsideration of achieving a balance between D_(uv) controllability andluminous efficacy of radiation. In other words, a phosphor materialhaving an emission peak in a long wavelength range from Λ3 (590 nm) to780 nm in the present invention has a peak that is favorably between 590nm and 600 nm and more favorably around 600 nm to 780 nm, and a peakwavelength is extremely favorably close to 630 nm. In particular, aphosphor material with a peak wavelength ranging from 620 nm to 655 nmis extremely favorable.

As for specific examples of the long wavelength range phosphor materialused in the illumination method or the light-emitting device accordingto the present invention, any phosphor material satisfying thefull-width at half-maximum described above can be favorably used. Inaddition, such specific examples include phosphors using Eu²⁺ as anactivator and a crystal constituted by alkaline-earth silicon-nitride, αSiAlON, or alkaline-earth silicate as a host. A red phosphor of thistype can normally be excited using a semiconductor light-emittingelement ranging from ultraviolet to blue. Specific examples of phosphorsusing an alkaline-earth silicon-nitride crystal as a host include aphosphor represented by (Ca,Sr,Ba,Mg)AlSiN₃:Eu and/or(Ca,Sr,Ba)AlSiN₃:Eu (this phosphor is referred to as a SCASN phosphor),a phosphor represented by (CaAlSiN₃)_(1-x) (Si₂N₂O)_(x):Eu (where xsatisfies 0<x<0.5) (this phosphor is referred to as a CASON phosphor), aphosphor represented by (Sr,Ca,Ba)₂Al_(x)Si_(5-x)O_(x)N_(8-x):Eu (where0≤x≤2), and a phosphor represented byEu_(y)(Sr,Ca,Ba)_(1-y):Al_(1+x)Si_(4-x)O_(x)N_(7-x) (where 0≤x<4,0≤y<0.2).

Other examples include a Mn⁴⁺-activated fluoride complex phosphor. AMn⁴⁺-activated fluoride complex phosphor is a phosphor which uses Mn⁴⁺as an activator and a fluoride complex salt of an alkali metal, amine,or an alkaline-earth metal as a host crystal. Fluoride complex saltswhich form the host crystal include those whose coordination center is atrivalent metal (B, Al, Ga, In, Y, Sc, or a lanthanoid), a tetravalentmetal (Si, Ge, Sn, Ti, Zr, Re, or Hf), and a pentavalent metal (V, P,Nb, or Ta), and the number of fluorine atoms coordinated around thecenter ranges from 5 to 7.

A favorable Mn⁴⁺-activated fluoride complex phosphor isA_(2+x)M_(y)Mn_(z)F_(n) (where A is Na and/or K; M is Si and Λ1; and−1≤x≤1 and 0.9≤y+z≤1.1 and 0.001≤z≤0.4 and 5≤n≤7) which uses ahexafluoro complex of an alkali metal as a host crystal. Among theabove, particularly favorable are phosphors in which A is one or moretypes selected from K (potassium) or Na (sodium) and M is Si (silicon)or Ti (titanium), such as K₂SiF₆:Mn (this phosphor is referred to as aKSF phosphor) or K₂Si_(1-x)Na_(x)Al_(x)F₆:Mn,K₂TiF₆:Mn (this phosphor isreferred to as a KSNAF phosphor) that is obtained by replacing a part(favorably, 10 mol % or less) of the components of K₂SiF₆:Mn with Λ1 andNa.

Other examples include a phosphor represented by the following generalformula (7) and a phosphor represented by the following general formula(7)′

(La_(1-x-y),Eu_(x),Ln_(y))₂O₂S  (7)

(In the general formula (7), x and y denote numbers respectivelysatisfying 0.02≤x≤0.50 and 0≤y≤0.50, and Ln denotes at least onetrivalent rare-earth element among Y, Gd, Lu, Sc, Sm, and Er). (Alanthanum oxysulfide phosphor represented by the general formula (7) isreferred to as an LOS phosphor).

(k−x)MgO.xAF₂.GeO₂ :yMn⁴⁺  (7)′

(In the general formula (7)′, k, x, and y denote numbers respectivelysatisfying 2.8≤k≤5, 0.1≤x≤0.7, and 0.005≤y≤0.015, and A is any ofcalcium (Ca), strontium (Sr), barium (Ba), zinc (Zn), and a mixtureconsisted of these elements). (A germanate phosphor represented by thegeneral formula (7)′ is referred to as an MGOF phosphor).

Among the phosphors described above, favorable examples include a LOSphosphor, an MGOF phosphor, a KSF phosphor, a KSNAF phosphor, a SCASNphosphor, a CASON phosphor, a (Sr,Ca,Ba)₂Si₅N₈:Eu phosphor, and a(Sr,Ca,Ba)AlSi₄N₇ phosphor.

In the illumination method or the light-emitting device according to thepresent invention, no particular restrictions are applied to materialsfor appropriately controlling a spectral power distribution of thelight-emitting device. However, it is extremely favorable to realize alight-emitting device such as those described below.

It is favorable to use a purple LED (with a peak wavelength of around395 nm to 420 nm) as a short wavelength range light-emitting element,and further incorporate at least one or more phosphors selected from agroup of relatively narrow band phosphors consisting of SBCA, SCA, andBAM in a light source as a light-emitting element in the shortwavelength range, incorporate at least one or more phosphors selectedfrom a group of relatively narrow band phosphors consisting of β-SiAlON,BSS, BSON, and G-BAM in the light source as a light-emitting element inthe intermediate wavelength range, and incorporate at least one or morephosphors selected from the group consisting of CASON, SCASN, LOS, KSF,and KSNAF in the light source as a light-emitting element in the longwavelength range.

A further description is given below.

It is extremely favorable to use a purple LED (with a peak wavelength ofaround 395 nm to 420 nm) as a first light-emitting element in the shortwavelength range, further incorporate SBCA that is a relatively narrowband phosphor in a light source as a second light-emitting element inthe short wavelength range, use β-SiAlON that is a relatively narrowband phosphor as a first light-emitting element in the intermediatewavelength range, and use CASON as a first light-emitting element in thelong wavelength range.

In addition, it is extremely favorable to use a purple LED (with a peakwavelength of around 395 nm to 420 nm) as a first light-emitting elementin the short wavelength range, further incorporate SCA that is arelatively narrow band phosphor in a light source as a secondlight-emitting element in the short wavelength range, include β-SiAlONthat is a relatively narrow band phosphor as a first light-emittingelement in the intermediate wavelength range, and use CASON as a firstlight-emitting element in the long wavelength range.

Furthermore, it is extremely favorable to use a purple LED (with a peakwavelength of around 395 nm to 420 nm) as a first light-emitting elementin the short wavelength range, further incorporate BAM that is arelatively narrow band phosphor in a light source as a secondlight-emitting element in the short wavelength range, use BSS that is arelatively narrow band phosphor as a first light-emitting element in theintermediate wavelength range, and use CASON as a first light-emittingelement in the long wavelength range.

Meanwhile, it is favorable to use a bluish purple LED (with a peakwavelength of around 420 nm to 455 nm) and/or a blue LED (with a peakwavelength of around 455 nm to 485 nm) as a short wavelength rangelight-emitting element, incorporate at least one or more phosphorsselected from a group of relatively narrow band phosphors consisting ofβ-SiAlON, BSS, BSON, and G-BAM in a light source as a light-emittingelement in the intermediate wavelength range, and incorporate at leastone or more phosphors selected from the group consisting of CASON,SCASN, LOS, KSF, and KSNAF in the light source as a light-emittingelement in the long wavelength range.

A further description is given below.

It is extremely favorable to use a bluish purple LED (with a peakwavelength of around 420 nm to 455 nm) and/or a blue LED (with a peakwavelength of around 455 nm to 485 nm) as a light-emitting element inthe short wavelength range, further use BSON that is a relatively narrowband phosphor as a first light-emitting element in the intermediatewavelength range, and use SCASN as a first light-emitting element in thelong wavelength range.

It is extremely favorable to use a bluish purple LED (with a peakwavelength of around 420 nm to 455 nm) and/or a blue LED (with a peakwavelength of around 455 nm to 485 nm) as a light-emitting element inthe short wavelength range, further use β-SiAlON that is a relativelynarrow band phosphor as a first light-emitting element in theintermediate wavelength range, and use CASON as a first light-emittingelement in the long wavelength range.

It is extremely favorable to use a bluish purple LED (with a peakwavelength of around 420 nm to 455 nm) and/or a blue LED (with a peakwavelength of around 455 nm to 485 nm) as a light-emitting element inthe short wavelength range, further use β-SiAlON that is a relativelynarrow band phosphor as a first light-emitting element in theintermediate wavelength range, use CASON as a first light-emittingelement in the long wavelength range, and use KSF or KSNAF as a secondlight-emitting element in the long wavelength range.

It is extremely favorable to use a bluish purple LED (with a peakwavelength of around 420 nm to 455 nm) and/or a blue LED (with a peakwavelength of around 455 nm to 485 nm) as a light-emitting element inthe short wavelength range, further use β-SiAlON that is a relativelynarrow band phosphor as a first light-emitting element in theintermediate wavelength range, and use SCASN as a first light-emittingelement in the long wavelength range.

It is extremely favorable to use a bluish purple LED (with a peakwavelength of around 420 nm to 455 nm) and/or a blue LED (with a peakwavelength of around 455 nm to 485 nm) as a light-emitting element inthe short wavelength range, further use β-SiAlON that is a relativelynarrow band phosphor as a first light-emitting element in theintermediate wavelength range, use SCASN as a first light-emittingelement in the long wavelength range, and use KSF or KSNAF as a secondlight-emitting element in the long wavelength range.

With the combinations of light-emitting elements described above, peakwavelength positions, full-widths at half-maximum, and the like of therespective light-emitting elements are extremely advantageous inrealizing a color appearance or an object appearance perceived asfavorable by the subjects in the visual experiments.

In the illumination method or the light-emitting device according to thepresent invention, it is favorable to use the light-emitting elements(light-emitting materials) heretofore described because the indexA_(cg), the luminous efficacy of radiation K (lm/W), D_(uv), and thelike can be more readily set to desired values. Using the light-emittingelements described above is also favorable because |Δh_(n)|,

$\begin{matrix}\left\lbrack {{Expression}\mspace{14mu} 32} \right\rbrack & \; \\{\frac{\sum\limits_{n = 1}^{15}{\Delta \; C_{n}}}{15},} & \;\end{matrix}$

ΔC_(n), and (|ΔC_(max)−ΔC_(min)|) which are related, when light istreated as a color stimulus, to a difference between color appearancesof the 15 color samples when illumination by the light-emitting deviceis assumed and color appearances when illumination by calculationalreference light is assumed can also be more readily set to desiredvalues.

Various means are conceivable for lowering D_(uv) from zero to setD_(uv) to an appropriate negative value. For example, when alight-emitting device having one light-emitting element in each of thethree wavelength ranges is assumed, an emission position of thelight-emitting element in the short wavelength range can be moved towarda shorter wavelength side, an emission position of the light-emittingelement in the long wavelength range can be moved toward a longerwavelength side, an emission position of the light-emitting element inthe intermediate wavelength range can be displaced from 555 nm.Furthermore, a relative emission intensity of the light-emitting elementin the short wavelength range can be increased, a relative emissionintensity of the light-emitting element in the long wavelength range canbe increased, a relative emission intensity of the light-emittingelement in the intermediate wavelength range can be decreased, or thelike. In doing so, in order to vary D_(uv) without varying the CCT, theemission position of the light-emitting element in the short wavelengthrange may be moved toward a shorter wavelength side and, at the sametime, the emission position of the light-emitting element in the longwavelength range may be moved toward a longer wavelength side, or thelike. Moreover, operations opposite to those described above may beperformed to vary D_(uv) toward a positive side.

In addition, when a light-emitting device respectively having twolight-emitting elements in each of the three wavelength ranges isassumed, D_(uv) can be lowered by, for example, increasing a relativeintensity of a light-emitting element on a relatively shorter wavelengthside among the two light-emitting elements in the short wavelengthrange, increasing a relative intensity of a light-emitting element on arelatively longer wavelength side among the two light-emitting elementsin the long wavelength range, or the like. In doing so, in order to varyD_(uv) without varying the CCT, the relative intensity of thelight-emitting element on a relatively shorter wavelength side among thetwo light-emitting elements in the short wavelength range is increasedand, at the same time, the relative intensity of the light-emittingelement on a relatively longer wavelength side among the twolight-emitting elements in the long wavelength range is increased.Moreover, operations opposite to those described above may be performedto vary D_(uy) toward a positive side.

Meanwhile, as means for varying |Δh_(n)|,

$\begin{matrix}\left\lbrack {{Expression}\mspace{14mu} 33} \right\rbrack & \; \\{\frac{\sum\limits_{n = 1}^{15}{\Delta \; C_{n}}}{15},} & \;\end{matrix}$

ΔC_(n), and (|ΔC_(max)−ΔC_(min)|) which are related to a differencebetween color appearances of the 15 color samples when illumination bythe light-emitting device is assumed and color appearances whenillumination by calculational reference light is assumed and, inparticular, as means for increasing ΔC_(n), operations such as describedbelow can be performed after adjusting an entire spectral powerdistribution so that D_(uv) assumes a desired value. Operations whichmay be performed include replacing each light-emitting element with amaterial having a narrow full-width at half-maximum, forming a spectrumshape in which light-emitting elements are appropriately separated fromeach other, installing a filter that absorbs a desired wavelength in anillumination light source, a lighting fixture, or the like in order toform a concave and/or a convex shape in a spectrum of eachlight-emitting element, and additionally mounting a light-emittingelement which performs emission at a narrower band in a light-emittingelement.

As described above, the present invention reveals a primary illuminationmethod or a primary light-emitting device for producing, with respect toa wide variety of illuminated objects with various hues, a colorappearance or an object appearance which is as natural, vivid, highlyvisible, and comfortable as though perceived in a high-illuminanceenvironment such as outdoors where illuminance exceeds 10000 lx, withinan illuminance range of approximately 150 lx to approximately 5000 lxfor which visual experiments have been carried out. In particular, theillumination method or the light-emitting device according to thepresent invention provides respective hues with natural vividness and,at the same time, enables white objects to be perceived more whiter ascompared to experimental reference light.

Means according to the illumination method of the present invention forproducing a color appearance or an object appearance which is asnatural, vivid, highly visible, and comfortable as perceived in ahigh-illuminance environment involve setting D_(uv) of light at aposition of an illuminated object to within an appropriate range and, atthe same time, setting indices related to a difference between colorappearances of the 15 color samples when illumination by the light isassumed and color appearances when illumination by calculationalreference light is assumed such as |Δh_(n)|,

$\begin{matrix}\left\lbrack {{Expression}\mspace{14mu} 34} \right\rbrack & \; \\{\frac{\sum\limits_{n = 1}^{15}{\Delta \; C_{n}}}{15},} & \;\end{matrix}$

ΔC_(n), and (|ΔC_(max)−ΔC_(min)|) to within appropriate ranges.

In other words, the illumination method according to the presentinvention is an illumination method of illuminating light in which aspectral power distribution thereof includes light emitted from asemiconductor light-emitting element as a component and in which|Δh_(n)|,

$\begin{matrix}\left\lbrack {{Expression}\mspace{14mu} 35} \right\rbrack & \; \\{\frac{\sum\limits_{n = 1}^{15}{\Delta \; C_{n}}}{15},} & \;\end{matrix}$

ΔC_(n), (|ΔC_(max)−ΔC_(min)|), D_(uvSSL), and the like are withinappropriate ranges to an illuminated object, and a light-emitting deviceused in the illumination method according to the present invention canbe configured in any way as long as the device is capable of providingsuch illumination. For example, the device may be any of an individualillumination light source, an illuminating module in which at least oneor more of the light sources is mounted on a heatsink or the like, and alighting fixture in which a lens, a light-reflecting mechanism, adriving electric circuit, and the like are added to the light source orthe module. Furthermore, the device may be a lighting system which is acollection of individual light sources, individual modules, individualfixtures, and the like and which at least has a mechanism for supportingsuch components.

In addition, the light-emitting device according to the presentinvention is a light-emitting device in which means for producing acolor appearance or an object appearance which is as natural, vivid,highly visible, and comfortable as perceived in a high-illuminanceenvironment involve setting D_(uv) as obtained from a spectral powerdistribution of light emitted in a main radiant direction to within anappropriate range and, at the same time, setting the index A_(cg) towithin an appropriate range.

In other words, the light-emitting device according to the presentinvention may be configured in any way as long as the light-emittingdevice includes light emitted from a semiconductor light-emittingelement as a spectral component in a spectral power distribution in amain radiant direction and in which D_(uv) derived from a spectral powerdistribution of light which is in the radiant direction and the indexA_(cg) are in appropriate ranges. For example, the device may be any ofan individual illumination light source, an illuminating module in whichat least one or more of the light sources is mounted on a heatsink orthe like, and a lighting fixture in which a lens, a light-reflectingmechanism, a driving electric circuit, and the like are added to thelight source or the module. Furthermore, the device may be a lightingsystem which is a collection of individual light sources, individualmodules, individual fixtures, and the like and which at least has amechanism for supporting such components.

INDUSTRIAL APPLICABILITY

The illumination method or the light-emitting device such as anillumination light source, a lighting fixture, a lighting system, andthe like according to the present invention has an extremely wide fieldof application and may be used without being limited to particular uses.However, in consideration of the features of the illumination method orthe light-emitting device according to the present invention, theillumination method or the light-emitting device according to thepresent invention is favorably applied to the following fields.

For example, when illuminated by the illumination method or thelight-emitting device according to the present invention, white may beperceived as being whiter, more natural, and more comfortable ascompared to a conventional illumination method or a conventionallight-emitting device even at a similar CCT and a similar illuminance.Furthermore, differences in lightness among achromatic colors such aswhite, gray, and black become more visible.

As a result, for example, black letters or the like on an ordinary sheetof white paper become more legible. To utilize such features, favorableapplications include a reading light, lighting for a writing desk, andwork lighting such as office lighting. In addition, while work mayconceivably involve performing a visual external examination of fineparts, distinguishing between near colors of cloth or the like, checkingcolor in order to verify freshness of meat, performing a productinspection by comparing with a criteria sample, and the like at afactory or the like, illumination by the illumination method accordingto the present invention makes color identification among close hueseasier and realizes a work environment that is as comfortable as thoughin a high-illuminance environment. Even from such a perspective,applications to work lighting are favorable.

Furthermore, since color discrimination ability increases, for example,applications to medical lighting such as a light source for surgicaloperations and a light source used in a gastroscope or the like are alsofavorable. While arterial blood is vivid red due to its high oxygencontent, venous blood is dark red due to its high carbon dioxidecontent. Although arterial blood and venous blood are both red, chromasof the colors differ from each other. Therefore, with the illuminationmethod or device according to the present invention which achievesfavorable color appearance (chroma), it is expected that arterial bloodand venous blood can be readily distinguished from each other. Inaddition, since it is obvious that favorable color representation incolor image information such as an endoscope has a significant effect ondiagnosis, it is expected that a normal location and a lesion locationcan be readily distinguished from each other. Due to similar reasons,the illumination method can be favorably applied to an illuminationmethod inside industrial devices such as a product image judgmentdevice.

When illuminated by the illumination method or the light-emitting deviceaccording to the present invention, a truly natural color appearance asthough viewed under several tens of thousands of lx such as outdoorilluminance on a sunny day is achieved for a majority of, and in somecases, all colors such as purple, bluish purple, blue, greenish blue,green, yellowish green, yellow, reddish yellow, red, and reddish purpleeven when illuminance only ranges from around several thousand lx toseveral hundred lx. In addition, the skin color of the subjects(Japanese), various foods, clothing, wood colors, and the like whichhave intermediate chroma also acquire natural color appearances whichmany of the subjects feel more favorable.

Therefore, by applying the illumination method or the light-emittingdevice according to the present invention to ordinary lighting for homesand the like, it is conceivable that food may appear fresher and moreappetizing, newspapers, magazines, and the like may become more legible,and visibility of differences in level in the house may increase,thereby contributing to improving home safety. Accordingly, the presentinvention is favorably applied to home lighting. In addition, thepresent invention is also favorable as exhibit lighting for clothing,food, vehicles, suitcases, shoes, ornaments, furniture, and the like,and enables lighting which makes such items stand out from theirsurroundings. The present invention is also favorable as lighting forgoods such as cosmetics in which slight differences in color are thedecisive factor when purchasing the goods. When used as exhibit lightingfor white dresses and the like, since subtle differences in color becomemore visible such as a difference between bluish white and creamy whiteamong similar whites, a person can select a color that is exactlyaccording to his or her desire. Furthermore, the present invention isalso favorable as presentation lighting at a wedding center, a theater,and the like, and enables a pure white dress or the like to be perceivedas being pure white and kimonos, makeup, in kabuki or the like to appearvividly. The present invention also favorably highlights skin tones. Inaddition, by using the present invention as lighting in a hair salon,colors that are no different than those perceived outdoors can beobtained during hair coloring and excessive dyeing or insufficientdyeing can be prevented.

Furthermore, since white appears more white, achromatic colors can bereadily distinguished, and chromatic colors attain their naturalvividness, the present invention is also favorable as a light source ina location where a wide variety of activities are conducted in a givenlimited space. For example, passengers in an airplane read, work, andeat at their seats. Similar situations take place on a train, along-distance bus, and the like. The present invention is favorablyapplicable as interior lighting in such public transport.

In addition, since white appears more white, achromatic colors can bereadily distinguished, and chromatic colors attain their naturalvividness, the present invention enables paintings and the like in anart museum or the like to be illuminated in a natural tone as thoughviewed outdoors and is therefore also favorable as lighting for works ofart.

On the other hand, the present invention is also favorably applicable aslighting for aged persons. In other words, even in case where smallcharacters are hard to read and difference in levels or the like arehard to see under normal illuminance, by applying the illuminationmethod or the light-emitting device according to the present invention,such problems can be solved since achromatic colors and chromatic colorscan be readily distinguished from one another. Therefore, the presentinvention is also favorably applicable to lighting in public facilitiesor the like which are used by the general public such as a waiting roomin a retirement house or a hospital, a book store, anda library.

Furthermore, the illumination method or the light-emitting deviceaccording to the present invention can be favorably used in applicationsfor securing visibility by adapting to an illumination environment inwhich illuminance is often at a relatively low level due to variouscircumstances.

For example, the illumination method or the light-emitting deviceaccording to the present invention is favorably applied to street lamps,head lights of vehicles, and foot lamps to increase visibility ascompared to using conventional light sources.

While the invention has been described in detail and with reference tospecific embodiments thereof, it will be apparent to one skilled in theart that various changes and modifications can be made therein withoutdeparting from the spirit and scope thereof.

1-88. (canceled) 89: A light-emitting device comprising at least abluish purple or blue semiconductor light-emitting element as alight-emitting element, wherein the light emitted from thelight-emitting device in a main radiant direction satisfies (1)′ and (2)below: (1)′ if an a* value and a b* value in CIE 1976 L*a*b* color spaceof 15 Munsell renotation color samples from #01 to #15 listed below whenmathematically assuming illumination by the light emitted from thelight-emitting device in the radiant direction are respectively denotedby a*_(nSSL) and b*_(nSSL) (where n is a natural number from 1 to 15),and an a* value and a b* value in CIE 1976 L*a*b* color space of the 15Munsell renotation color samples when mathematically assumingillumination by a reference light that is selected according to acorrelated color temperature T_(SSL) (K) of the light emitted from thelight-emitting device in the radiant direction are respectively denotedby a*_(nref) and b*_(nref) (where n is a natural number from 1 to 15),then each saturation difference ΔC_(n) satisfies−3.8≤ΔC _(n)≤18.6 (where n is a natural number from 1 to 15); if amaximum saturation difference value is denoted by ΔC_(max) and a minimumsaturation difference value is denoted by ΔC_(min), then a difference|ΔC_(max)−ΔC_(min)| between the maximum saturation difference value andthe minimum saturation difference value satisfies2.8≤|ΔC _(max) −ΔC _(min)|≤19.6, whereΔC_(n)=√{(a*_(nSSL))²+(b*_(nSSL))²}−√{(a*_(nref))²+(b*_(nref))²} withthe 15 Munsell renotation color samples being: #01 7.5P 4/10 #02 10PB4/10 #03 5PB 4/12 #04 7.5B 5/10 #05 10BG 6/8 #06 2.5BG 6/10 #07 2.5G6/12 #08 7.5GY 7/10 #09 2.5GY 8/10 #10 5Y 85/12 #11 10YR 7/12 #125YR7/12 #13 10R 6/12 #14 5R 4/14 #15 7.5RP 4/12; and (2) if hue anglesin a CIE 1976 L*a*b* color space of the 15 Munsell renotation colorsamples when mathematically assuming illumination by the light emittedfrom the light-emitting device in the radiant direction is denoted byθ_(nSSL) (degrees) (where n is a natural number from 1 to 15), and hueangles in a CIE 1976 L*a*b* color space of the 15 Munsell renotationcolor samples when mathematically assuming illumination by a referencelight that is selected according to the correlated color temperatureT_(SSL) (K) of the light emitted in the radiant direction are denoted byθ_(nref) (degrees) (where n is a natural number from 1 to 15), then anabsolute value of each difference in hue angles |Δh_(n)| satisfies0≤|Δh _(n)|≤9.0 (degrees) (where n is a natural number from 1 to 15),where Δh _(n)=θ_(nSSL)−θ_(nref). 90: The light-emitting device accordingto claim 89, wherein the light emitted from the light-emitting device inthe radiant direction further satisfies (1)″ below: (1)″ an averagesaturation difference represented by formula (1) below satisfies formula(2) below: $\begin{matrix}{\frac{\sum\limits_{n - 1}^{15}{\Delta \; C_{n}}}{15},} & (1) \\{1.0 \leqq \frac{\sum\limits_{n = 1}^{15}{\Delta \; C_{n}}}{15} \leqq {7.0.}} & (2)\end{matrix}$ 91: The light-emitting device according to claim 89,wherein the correlated color temperature T_(SSL) (K) satisfies2550 (K)≤T _(SSL) (K)≤7000 (K). 92: The light-emitting device accordingto claim 89, wherein if a spectral power distribution of the lightemitted from the light-emitting device in the radiant direction isdenoted by φ_(SSL)(λ), a luminous efficacy of radiation K (lm/W) in awavelength range from 380 nm to 780 nm as derived from the spectralpower distribution φ_(SSL)(λ) of light emitted from the light-emittingdevice in the radiant direction satisfies180 (lm/W)≤K (lm/W)≤320 (lm/W). 93: The light-emitting device accordingto claim 89, wherein illuminance at which the light emitted from thelight-emitting device in the radiant direction illuminates objects is150 lx to 5000 lx. 94: The light-emitting device according to claim 89,wherein the light-emitting device emits, in the radiant direction, lightemitted from one to six light-emitting elements including the lightemitted by the semiconductor light-emitting element. 95: Thelight-emitting device according to claim 89, wherein a peak wavelengthof an emission spectrum of the semiconductor light-emitting element is420 nm or longer and shorter than 455 nm. 96: The light-emitting deviceaccording to claim 89, wherein a peak wavelength of an emission spectrumof the semiconductor light-emitting element is 455 nm or longer andshorter than 485 nm. 97: The light-emitting device according to claim89, comprising a phosphor as a light-emitting element. 98: Thelight-emitting device according to claim 97, wherein the phosphorincludes one to five phosphors each having different emission spectra.99: The light-emitting device according to claim 97, wherein thephosphor includes a green phosphor and a red phosphor. 100: Thelight-emitting device according to claim 99, wherein the green phosphorincludes a green phosphor having an individual emission spectrum, whenphotoexcited at room temperature, with a peak wavelength of 495 nm orlonger and shorter than 590 nm and a full-width at half-maximum of 2 nmto 130 nm. 101: The light-emitting device according to claim 99, whereinthe red phosphor includes a red phosphor having an individual emissionspectrum, when photoexcited at room temperature, with a peak wavelengthof 590 nm or longer and shorter than 780 nm and a full-width athalf-maximum of 2 nm to 130 nm. 102: The light-emitting device accordingto claim 99, wherein the green phosphor includes a narrow band greenphosphor. 103: The light-emitting device according to claim 99, whereinthe green phosphor includes β-SiAlON. 104: The light-emitting deviceaccording to claim 99, wherein the red phosphor includes SCASN.